BMW i3 Long Term Battery Capacity Report: Better Than Expected

7 months ago by Tom Moloughney 101

The author’s (very unique in red) BMW i3

When it comes to electric cars, it’s all about the battery. Well, it’s not quite that simple, but given how important the battery is to the cost, range and performance of the vehicle, it’s pretty close.

When someone is considering purchasing their first electric car, they will certainly have a lot of questions.

The one question that seems to be on nearly everyone’s list is: “How long will the battery last?”

The problem is, it’s been very hard to answer that question authoritatively because we just haven’t had enough data.  That’s because modern electric cars that are powered by high-voltage lithium ion battery packs have been on sale for less than ten years, and long term testing results simply weren’t available.  In fact, the Nissan LEAF was the first high-volume all-electric car brought to market, and that model has only been on sale for a little over six years.

Nissan’s early LEAF battery woes:

As A Solution To Early Battery Woes, Nissan’s Introduced A New Pack Replacement Program While The EV Was Under Warranty, Which Guaranteed At Least “9 Bars” Of Performance (70% of original).

Some of the early Nissan LEAFs had premature battery degradation issues, particularly those that were in service in hot climate areas like Arizona.

It became such a problem that Nissan changed the chemistry of their batteries in 2015 to a more temperature-tolerant version and announced an improved battery warranty to ease the concerns of current owners and future buyers.

The negative press from this problem threatened to set back the advancement of all makes of electric cars, because it brought to light the possibility of EV battery packs failing earlier than previously predicted.  However, this was a self-inflicted wound, in my opinion. Nissan elected to bring the LEAF to market with a simple air-cooled battery pack, instead of employing a sophisticated liquid-based system like Tesla and GM were already using back then. The decision to do so allowed for a lower MSRP, as well as a shorter R&D period, but most likely contributed to the early degradation problems that some LEAF owners experienced.

GM’s family of batteries: Left to right: a first generation Volt, a second generation Volt, and a Spark EV, and a 60 kWh Bolt EV pack (Photo by Jeffrey Sauger for General Motors)

Tesla & GM batteries performing well:

Fortunately, the other mass-market EV manufacturers that launched their respective cars earlier in the decade have not had the same battery degradation issues that Nissan experienced. Both the Chevrolet Volt and the Tesla Model S have complex, liquid-based thermal management systems and the battery packs of both of these vehicles seem to be holding up very well over time.

In fact, Plug In America has been collecting data from hundreds of high-mileage Model S owners, and has built a database of battery degradation rates. They’ve found that the average Model S owner is experiencing a loss of only 2.3 miles of range for every 10,000 miles driven.  Considering all Tesla vehicles offer more than 200 miles of range, an estimated loss of only 23 miles of range for every 100,000 miles of driving is very good. Obviously that the rate of 2.3 miles of loss per 10,000 will likely accelerate at some point, because battery capacity loss isn’t linear, but all of the vehicles in the study had more than 50,000 miles. That made them good candidates to study the loss of range over time.  General Motors has similarly reported no problems with Volt battery packs experiencing early capacity loss.

How has the BMW i3 held up after 70,000+ miles?

How’s my BMW i3’s battery holding up?

BMW launched their first retail all-electric car, the i3 in Europe in late 2013. Here in the North America, the first i3 deliveries started in May of 2014. I actually took delivery of the first i3 REx in the US and I drive more than the average person, so I have one of the highest mileage i3s on the road.

I’m a couple weeks shy of my three-year anniversary with the car and I have 70,000 miles on the odometer. I know I’m only one sample, but if what I’ve experienced turns out to be the norm, then i3 owners are going to be very happy with how their battery holds up over time.

BMW is one of the few EV manufacturers that offer a clear battery capacity loss warranty, and has guaranteed at least 70% capacity for 8 years or 100,000 miles. The stated usable capacity for the 2014 i3 is 18.8 kWh. Therefore, the battery would need to degrade to 13.15 kWh to trigger a warranty claim.

Tom’s BMW i3

Methods used to arrive at my conclusion

I’ve found that even though the range estimator does a pretty good job for daily driving, it’s not nearly accurate enough to use for recording and documenting the true range of the vehicle. Instead, I have two other types of data points that helped form the basis of my conclusions regarding the current state of health of my battery.

The ever-optimistic “GOM”

First, I frequently record my trip mileage and remaining state of charge before I plug in. This gives me a more accurate view of how far I can go per charge than what the range estimator provides. (Frequently called the GOM or Guess-O-Meter by some EV enthusiasts) The fact that I have an i3 with range extender complicates it a little, because the range extender turns on when the SOC in under 7%. Therefore, I only have access to 93% of the usable capacity of the battery before the REx fires up.  

The simple formula I use is arrived at by dividing the number of miles driven by the percentage of battery used. That value will be how many miles (or what percentage of 1 mile) the car has traveled for every 1% of battery used.  I then need to multiply that by .93 (100% minus the 7% buffer) and I then have how many miles the car would have been able to go if I had continued driving until the REx turned on.

Examples:

  • Starting SOC: 100%
  • Ending SOC: 45%
  • SOC used: 55%
  • Miles driven: 45
  • (45/55) x .93 = .76 (76 miles per charge)

 

  • Starting SOC: 92%
  • Ending SOC: 8%
  • SOC used: 84%
  • Miles driven: 67
  • (67/84) x .93 = .74 (74 miles per charge)

 

Cutaway Of BMW i3 Showing Battery Housing

When using this method to gauge battery performance it’s important to record the ambient temperature if you live in an area that experiences moderate to extreme cold and hot temperatures. These temperature swings will affect the car’s range. The cold weather has a much more dramatic effect than hot weather does, and it’s important to compare the present figures with past data from the same time of the year, when temperatures were similar.  

For the purpose of this comparison I’m stating figures that were gathered when the temperatures were between 60 degrees and 80 degrees, which is close to the optimum operating temperature range for the i3’s battery. For instance in the coldest months of the year, with temperatures below 20 degrees, my average electric range was as low as only 55 miles per charge.

Tom’s “BattKapaMax” showing good results

The second method I used involves the car’s onboard diagnostics tool meant for service personnel, called the hidden service menu. This offers an estimate of the battery’s state of health. The onboard computer calls it the “Batt.Kapa.Max” and it displays the amount of usable capacity (not total capacity) in kWh. This number isn’t exactly accurate – it’s an estimate, and I caution i3 owners from looking at it and treating it as a precise fact. In order to use this estimate to really help you understand and monitor your battery’s capacity, you need to check it frequently, and chart the readings on a graph. The number provided can swing as much as 2 kWh up or down on a daily basis, so it’s clearly not precise.

Don’t panic if you check it one day and the reading is unusually low. What I’ve found is that to get a good reading you should drain the battery as low as you can, and then check the reading once it’s fully recharged. The battery should also be as close to 70 degrees Fahrenheit, as colder temperature give a false reading that is slightly lower than the true value.  BMW has warned against relying on this since it is an estimate. The only way to get a truly accurate measurement (for warranty claims) is to have a BMW service department perform a test.

BMW claimed that the usable capacity for the 2014 – 2016 i3s was 18.8 kWh. However, some owners have seen as high as 19.9 kWh available when they’ve checked the Batt.Kapa.Max reading.

This can either be attributed to an inaccurately high reading (remember this is not a precise reading), or that BMW has actually opened up more than the 18.8 kWh they claim is available. The highest reading I have ever seen on my car was 19.2 kWh, and the lowest was 16.1 (in the winter). When my car was new the average reading in favorable conditions was about 19 kWh. Today, my average reading is now about 18.2 kWh. If these average readings are correct, it would mean that I’ve lost about .8 kWh of usable capacity after 36 months, 70,000 miles and approximately 1,000 complete charging cycles.  (I’ve probably plugged in closer to 2,000 times, but my average trip between plugging in is only about 37 miles).

Achieving 84 miles per charge is still attainable, as long as I drive conservatively and maintain a 5.0 or higher consumption rate

The .8 kWh loss of usable capacity seems to be in line with my recorded range data.  Since I’m averaging about 4 mi per kWh, I should be witnessing a loss of about 3 miles of range, (.8 x 4 = 3.2) which is exactly what my range readings have recorded.

When the car was new, I was averaging 78 miles per charge in favorable weather conditions; it’s now down to 75 miles per charge. That’s pretty impressive since the EPA range rating for the 2014 i3 REx was 72 miles per charge. So I’m still averaging more than the EPA range after three years and 70,000 miles.  Since both measurement methods equate to about a 4% capacity loss, I’m pretty confident that they validate each other. Therefore, the 4% is correct, or at least very close to the actual capacity loss

A 53 mile spin still shows 22 miles remaining

This should be very encouraging for existing i3 owners, and help to alleviate any anxiety that those currently considering the purchase of an i3 might have.

I have to believe that the sophisticated thermal management system that BMW used in the i3 is partially responsible for the excellent long-term performance of the Samsung battery cells used in the car.

If my experience holds true for the majority of the i3 fleet, this is good news not only for BMW, but also for the entire EV industry. Battery capacity loss concerns are on the minds of many potential consumers that are interested in entering into the world of electric cars. Continued positive reports on battery life will help to alleviate those worries and give the entire industry a boost of confidence.

However, as I said above my experience is just one data point, there’s a lot more information needed before we know conclusively how long these packs will last, but this indeed very encouraging. Based on my personal findings, I suspect that BMW won’t have to worry about paying out too many battery capacity-loss warranty claims.

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101 responses to "BMW i3 Long Term Battery Capacity Report: Better Than Expected"

  1. Jernej says:

    It’s not only mileage – cars should also last around 15 years – at least this is mine expectation. It means all current battery cars would need 2 packs of batteries during their lifetime.

    1. M Hovis says:

      Pretty open-ended statement so here is an open-ended response.

      US autos average lifecycle is around 11 years now. That translates to many like yourself with a 16-year life cycle and many with a much shorter. Of course, it doesn’t mean that the 16-year auto doesn’t have a really large service folder for regular maintenance.

      This is BMW’s first attempt at a production battery and it appears, as Tom qualifies with one data point, that it will exceed their stated promises. I think most Tesla, GM, and others are going to prove an easy 10-year cycle. If you want to ensure a 16-cycle, then purchase an i3 Rex like Tom did or a Chevy Volt EREV like I did to ensure that the EV keeps going for your 16-year desired cycle. As for the rest of the masses who don’t really care about that, I still think the general premise that Tom has laid down is a good one. IMO

      1. SparkEV says:

        Rex or PHV (you call it EREV) won’t save you much. If the battery goes, car will be worthless, more so than BEV. For example, if the battery dies after 11 years (out of warranty), and cost $12K to fix while used cars of same vintage cost only $3K, you wouldn’t spend so much money, instead of simply junking it.

        Compounding the problem for Rex/PHV that also carry gas engine is the gas engine. There’s a risk that should the gas engine fail after battery replacement, that could lead to another round of expensive repair.

        At least with BEV versions of the car with similar battery (i3 BEV, SparkEV), there’s no risk of gas engine going bad after the battery is replaced. I doubt may will opt to replace the battery on 11 year old car, but it makes more sense for BEV than PHV.

        1. BenG says:

          For some years there will be relatively affordable used, refurbished battery packs available to keep the older well-maintained, un-wrecked Leafs and Volts going in the event of a battery failure, IMO.

          1. SparkEV says:

            If rebuilt battery experience is anything like mine with Prius, most people won’t opt for that. It’s a huge risk, and something with poorly engineered battery (Leaf) or aging gas engine (Volt, i3Rex), it’s not worth it.

            Case could be made for BEV, but even that’s iffy when used BEV with lot more features and range could cost as much as battery replacement cost. I wouldn’t pay more to fix any of today’s BEV with less range/features than used car (EV or gasser) of similar price.

            1. C G says:

              I believe you are way off the mark regarding the REx engine. It simply isn’t used enough to “DIE” right after the user replaces the EV battery at 150k miles. Typical use on the REx is 10 of the miles, and it has scheduled maintenance once per year. (There’s already data on the engine life since it isn’t new.)

              The car won’t have any rust, and it shouldn’t need a new electric or gasoline engine. Even the brakes should last a really long time.

              Wish all cars were made of aluminum and CFRP…

              1. SparkEV says:

                Even if you don’t use the gas engine, it deteriorates. Seals leak, spark contacts oxidize, sensors deteriorate, etc. etc. For a 12 year old gas engine, even if not used much, it will need significant work: fluids changed, cap and rotor (tune up), maybe belts and hoses replaced.

                Short running ICE isn’t good. Combustion by-product (acids) get accumulated in oil which could’ve been burned off in longer running engine. Without periodic time based maintenance, the age of engine would matter more than how much it’s run. There are other drawbacks to short running ICE, such as more fuel when cold that could contribute to carbon build-up, though that’s lot longer term issue.

                1. cab says:

                  This is true, but only to a degree. I’ve spent a considerable amount of time recently working on my family’s fleet of used cars. At least three of them with >150K miles. One thing that really seems to impact these engines as they age is simply HEAT. Everything starts to go. Connectors are all as brittle as heck as is everything made of plastic and rubber. Electrical sensors also tend to give up the ghost quicker given the constant exposure to high underhood temps.

                  The average PHEV will have simply run the engine a LOT less at an equivalent mileage (heck, at 34K miles our gen 1 Volt had only run the engine for about 7k of those miles). Time isn’t nearly as huge an issue when the engine isn’t running!

                  1. SparkEV says:

                    It’s not only the heat, but the air. Air pollution does wonders in killing car stuff. Granted, it’s not as bad as before.

                    Still, I wouldn’t want to spend more than comparable used car price to replace a battery on a hybrid with old engine, little used or not.

                    1. Bill Howland says:

                      Since most cars have individual (or sometimes paired) ignition coils, I doubt you’ll see anything remotely like a ‘Cap and Rotor’.

                      Its uncanny how little maintenance most GM cars, and certainly the EREV’s require. Coolant change at 5 years (or 150k miles – same as the BOLT), tune up at around 100,000 miles. Fan Belt INSPECTION (not replacement) after 10 years, etc.

                      Dexos oil change every 2 years even if you don’t need it (most don’t, but I do it to keep the warranty in effect). Brake fluid replacement in 3-5 years, but apparently everyone ignores the Nissan Leaf annual requirement and their brakes still work.

            2. C G says:

              Should say 10% of miles.

            3. Terawatt says:

              I think the jury is still out. To the best of my knowledge nobodys been doing this in a scale that can reasonably be described as commercial.

              Battery cells don’t age all the same, but vary a lot individually. And it’s how deeply discharged the weakest cell is that determines when you must stop drawing power, as further use can otherwise kill that cell, and with it, the pack. Li-ion unfortunately is permanently destroyed by being fully depleted.

              I don’t have enough knowledge about this to do any calculations, but it does seem plausible to me that many LEAF packs may be given a new lease of life by replacing the one or two worst cells with new ones, or refurbished ones from a crashed/salvaged vehicle (which may have nearly a hundred cells in excellent condition).

              The labour cost is probably a significant hurdle, but I’m not sure how long a job like this would need to take given optimised equipment, nor what that equipment would be our how much it would cost. So there’s a lot that would have to change to make this viable, but I for one am not ready to say it can’t work.

              1. Warrren says:

                My 2017 was showing 29.7 kWh last time I checked. I need to check it in warmer weather to see if it varies as much. With the mild SoCal weather around here, the readout seems to be pretty consistent:

                FYI, I had my 2017 i3 at car show yesterday. Drove the Bolt for a good test run. I can honestly tell you the way I drive, the BOLT FWD traction is horrible. I was chirping and spinning tires, even at half throttle, to the point of embarrassment. By contrast you can full throttle the i3 almost anywhere without even a chirp from the tires while pulling similar 6.5 second 0-60 times with no drama whatsoever. And even on wet roads, the tire rarely spins. I also had a 6 ft, 400lb large guy fit in the drivers seat of the i3. I asked him to sit in the BOLT parked across from me. NO matter how hard he tried, he could not fit in the driver’s seat of the BOLT. He swore the BOLT seemed smaller and more cramped, contrary to what others report.

                Contrary to what I would have thought, the i3 also had twice as many people looking at it at both car shows this weekend, compared to the Bolt. With more people interested and asking questions about the i3. The guy from the California Clean Air Rebate Program also confirmed the i3 is the most fun EV to drive. Pretty interesting results.

                1. Pushmi-Pullyu says:

                  If the Bolt EV doesn’t use traction control to prevent the wheels from spinning, then that’s pretty shocking. I expect better from GM engineering.

                  Perhaps I was right to express concern about GM using an inexperienced company like LG Electronics’ new automotive division to build the Bolt EV’s powertrain. 😐

                  1. SparkEV says:

                    Traction control still result in chirps. That’s how SparkEV manage to leave nice two track tire marks on road. Basically, traction control kicks in after slipping a little, then release, repeat. Acceleration time is lousy because of it, but the little ecobox squealing the tires is pretty amusing.

                  2. WARREN says:

                    And, I forgot to mention, all this traction drama was with both hands tightly on the steering wheel, going straight ahead with traction control on. Really, it was that bad. I can’t imagine how much drama there would be coming out of a turn. I got 8000 miles on my FWD LEAF tires. I bet I wouldnt get 3000 on the BOLT tires. The i3 has no problems flooring the throttles out of turns either…so smooth not even a chirp.

        2. pjwood1 says:

          People home brewing storage systems report Volt batteries available for $1-2k. Why are you suggesting the car would be worthless, if it needed one? You can’t touch a diesel muffler, for that.

        3. Nero says:

          Where does 12k$ figure coming from? Even today to replace brand new battery in U.K. For Leaf cost just £5000-5500 with all labour included

        4. Peter says:

          Price for battery will drop in that period. You will be able to by a larger an better battery maybe at half the price. That will still be much cheaper then buying a new car.
          I will be happy with my Model S after 10 years and a new 100kW battery.

      2. Jernej says:

        I am not buying. I would guess cars in Germany are used even less time. But then they get sold in Poland (and similar) and eventually further east/south. My guess would be average car lifespan is more than 15 years. I agree with some commentators that falling battery prices might be of real help.

        We don’t have much data about battery degradation yet. There are cars with significant mileage, but there are practically no cars with old batteries AND significant mileage.

      3. Terawatt says:

        Nope. Cars last much longer than you think. The AVERAGE car on the road in the US is older than what you believe is the average LIFE of a car!

        https://www.google.no/amp/amp.usatoday.com/story/30821191/

        I don’t know why so many people are making the same mistake you just did, but maybe it’s simply that we tend to think we know stuff, so we don’t bother looking it up before repeating some misunderstanding we’ve read somewhere else.

        In any case, 11 years average life does seem extremely low, doesn’t it? As you say, it would mean lots of cars have much shorter lives than that. But a random 2010 car is typically I’m quite useable shape and not looking like it’s almost ready to be scrapped.

        1. Pushmi-Pullyu says:

          I do think we need to be careful to distinguish between “expected lifetime of the car” and “how long a car owner keeps the car”.

          There is a large segment of the population that never seriously considers buying a new car, for whom a “new car” means replacing a car they bought used with another used, but newer, car. That’s true even in the USA, and in some poorer countries, Mexico for example, the percentage of cars that are bought used is much higher.

          It seems to me the usual situation, for those who buy new cars, would be that if a BEV’s battery pack needs replacing, they would simply choose to buy a new car at that time. So anyone buying that car — either the second owner or a used car dealer, — would either have to accept a car with a battery pack that is significantly degraded, or else spring to replace the pack with a refurbished pack.

          I think it’s reasonable to expect replacing battery packs on used BEVs to grow as a cottage industry, or perhaps as a side business for salvage yards. Right now very few battery packs from wrecked BEVs are being salvaged or recycled; there will be a lot of potential there for replacing battery packs on used BEVs.

          I dunno about “refurbishing” them. What does that mean? Battery cells in a li-ion pack need to be carefully balanced, so it’s not like you can just tear a pack open and pop in some new cells. Any replacement of cells would have to be done very, very carefully, using cells which exactly match (in age and capacity loss as well as type) what’s already there, and by someone who knows exactly what he’s doing. Best not mess with the BMS (Battery Management System) and its proprietary software, either.

          No, I think the usual procedure for a “cottage industry” replacement would be to replace the battery pack with a used one as-is, disturbing the innards of the pack as little as possible, and hope for the best.

          It will be interesting to see what develops as people try to do that, what problems develop as a result, and what procedures are developed to deal with those problems.

    2. mx says:

      How do you figure this car will need 2 battery swaps, when the author lost 3 miles of range over 70,000 miles?
      That would be a 12 mile range loss over 280,000 miles.

      The current model range of 114 miles would mean a drop of about 14 miles for 300,000 miles: Going from a range of 114 to a range of 100.

      So, no battery swap needed, ever.

      1. Pushmi-Pullyu says:

        I think he meant just one replacement, not two.

        But yeah, if you need to replace the battery when the capacity loss is that low, then you probably bought the wrong BEV to begin with. You should have bought something with better range to start.

        Let’s do the math: If the average driver keeps the car 11 years and drives it 15,000 miles per year, that’s 165,000 miles. If the pack loses 3.2 miles for every 70,000, assuming linear loss, that would be a total loss of only 7.5 miles. So yeah, it seems quite unlikely that would call for a pack replacement, and keeping it for 15 years wouldn’t lose many more miles.

      2. Peter says:

        I agree that no battery swap is needed but newer battery’s will be cheaper and have more power at a lower cost maybe even lighter so buying a new battery will be the best option for most people that mainly drive to work and home every day.

    3. MaxEV says:

      The warranty is for 8 years which is longer than ICE power train warranty.

      For example, F-150 has a 7-year warranty does that mean that I need to replace my engine after 7 years? No.

    4. Great article Tom.

      One comment regarding driving tests used to measure battery capacity is to ensure it’s on a closed course.
      (ie: start and end points are the same, to reduce any energy potential difference associated with elevation)

    5. Pushmi-Pullyu says:

      “It means all current battery cars would need 2 packs of batteries during their lifetime.”

      Obviously it depends on how much capacity loss you’re willing to accept before replacing the battery pack. The consensus among Tesla Model S drivers seems to be that most think their original pack will last the lifetime of the car, but then the average person (or at least the average American) doesn’t keep a car for 15 years. If you do plan to keep it for 15 years, then you might well need to replace the pack during that time.

      This doesn’t apply to Leaf owners — all bets are off for them, and it’s too bad they bought a BEV with only passive battery cooling. 🙁

  2. stimpy says:

    Thankfully batteries get about 7% cheaper each year and they are designed to make swapping the battery a simply procedure. Much easier than say swapping a gas engine.

    Also the effect of swapping an original battery for a decade newer one would be like swapping out a 4 cylinder gas engine for an 8 cylinder, except the improvement will be in range instead of HP. 🙂

    Some will probably choose to do this to get increased range even if the battery capacity is still perfectly acceptable.

    1. mx says:

      Not only that but you could play with the percentages.
      You could increase your range by 50% and reduce the weight by 50%, and you could get More Range and More Effective HORSEPOWER, and torque, to the road.

      So, yes, in 10 years, you could get another second off your 0-60 times.

  3. stimpy says:

    And then, unlike a gas engin, you (or a second owner) could reuse that retired battery for low-stress usage such as battery backup power at your house.

    Anyway you look at it batteries seems to come out far ahead of gas engines.

  4. Carsten says:

    Well,
    I have a 2012 MiEV, that I purchased in June 2013. It has now 66,000mi on the odometer and I have about 40% battery degradation, according to the Mitsubishi Service Center. The MiEV has an air-cooled battery pack.I have 3 cells in the pack, that end up at a much lower cell voltage than all the others. Mitsubishi told me, that 40% at 66,000mi is normal and not a case for warranty. The warranty is 8years or 100,00mi, whichever comes first, but no stipulation on range loss.
    Here is to me hoping that one of the lower voltage cells will fail prior to 100,000mi.
    Not too happy about the battery, but love to drive electric.

    1. ClarksonCote says:

      Make your next EV a Bolt and you’ll never have to worry about battery loss or range again 😉

      You’ll love it’s drive compared to a miEV

      1. Carsten says:

        I’m looking into 2nd hand Spark EVs or Kia Souls as a bridge to a 2nd hand Bolt EV or Volt Gen2. I drive 35mi to work each way, half of it on DC-motorways, and the MiEV will still do for 1-2 years. I currently have about 50mi of range, when going to/from work.
        I’d love the Bolt, but it’s too expensive for what I need it for. Our other car is a 2001 RAV4 with 270,000mi, that will still do for a couple of years.

    2. alohart says:

      Our 2012 i-MiEV did not have the DC fast charging option which meant that its battery pack had only passive cooling like the Leaf (i.e., conductive cooling only with no forced air cooling). An i-MiEV with the DC fast charging option could turn on the A/C and divert its cool air outlet from the cabin to the battery pack during DC fast charging to help cool the battery pack. But when not DC fast charging, battery cooling was passive just like an i-MiEV without DC fast charging and a Leaf. So I’m not surprised that an i-MiEV’s battery pack is subject to faster heat-related degradation that a liquid-cooled pack like in our BMW i3 BEV.

      1. Carsten says:

        I have the version with the DC-Fast charging and it switches on for at least a little bit, even when I plug it into 110V or 240V. I use DC-charging probably onec or twice a month and only to 80%. The DC-charging switches of at that point.
        So, that’s not it. It might just be, that air-cooling and no pack heating in winter has that effect on the pack.

    3. SparkEV says:

      As I read it, iMiev is “air cooled” in that it’s cooled via blowing cool air from AC unit. It’s not air cooled in conventional sense that just blow ambient temperature air using a fan like Prius. Better term for iMiev might be active air cooled.

      Many people think Leaf and eGolf are air cooled, but they are not. VW calls it “passive cooled”, not sure if Nissan calls it any cooling; it’s just a sealed box. That’s why active air cooling is an important distinction for iMiev.

      I think you mean iMiev has lower pack voltage, not cell. iMiev has 3.7V nominal cell voltage, similar to 2015+ SparkEV, i3, Teslas, Volt, etc. 2014 SparkEV had LFP cells (like old Fisker) which has 3.2V nominal. However, iMiev has 88 cells in series, which makes the pack voltage to be 330V instead of about 360V for others. 2015 SparkEV has 96 series, 2014 SparkEV has 112 in series.

      1. Carsten says:

        I mean cell voltage. I have an app, that reads the cell data (voltage, temp) for all cells at any point in time.

        1. SparkEV says:

          What voltage do you read for cells? Google shows it should be 3.7V nominal.

          1. Carsten says:

            This morning at 99.5% SoC they were between 4.09 and 4.085V. 45min later at work at 43.5% SoC they were between 3.92 and 3.895V. The lower voltage cells after a drive are always the same. The whole pack had 360V at the start and 344V at the end.

      2. Good point about the term “air cooled”. Passive and active air cooling IS different, as you mention.

        1. SparkEV says:

          After thinking about it, I think even active cooling is wrong term for iMiev. Prius using a fan would be active air cooling while motorcycle engine without fan (but with cooling fins) would be passive air cooling.

          Bit long, but more accurate term for DCFC capable iMiev (and SoulEV) would be active AC air cooled.

          1. We could do an entire article on this…

            1. georgeS says:

              Yes Tom,

              You should add that BMW’s cooling scheme is unique. Instead of liquid cooing in the pack, BMW engineers use refrigerant like in your air conditioner.

              Good article. Sounds like your batts are holding up well.

              1. I actually had that in the article, George, but cut it out because it was getting too long. Like I said, we could (should?) do an entire article on thermal management systems.

                1. David S. says:

                  Absolutely should, including a table listing the cooling method for all EV models

    4. Terawatt says:

      Exactly! You’ve got 85 cells that are much better and 3 bad ones that determine the performance of the pack! This is one of the major advantages of string batteries – they allow you to use the full capacity of all cells regardless of their individual state, essentially by turning each cell into a module with onboard BMS.

      But it also means Mitsubishi could bring new life to 20 packs like yours using a single salvaged i-MiEV.

      The problem is basically that garages don’t have the knowhow or equipment to open up a pack and replace only the weakest cells.

      Maybe one day there will be enough EVs on the road that suffer from this problem (a few bad eggs) that it will be worthwhile for at least a few garages to invest in providing this type of service. I’m unsure how much labour would still be required (with the right equipment and people), but the battery cost side is definitely NOT a problem here. You only need five percent of a pack after all.

    5. Pushmi-Pullyu says:

      “Mitsubishi told me, that 40% at 66,000mi is normal and not a case for warranty.”

      Seems like a pretty shocking loss to me to be considered “normal”. That’s even worse than what many Leaf owners have reported.

      I realize that degradation over time is partly dependent on the size of the battery pack — smaller packs will degrade faster, all else being equal, because they get cycled more often — but IMHO it still shows how inferior passive cooling is.

      1. Carsten says:

        It’s active cooling. The AC switches on every time I DC-charge and also most of the time, when I charge on 240V.

  5. One says:

    Thank you Tom, for your many contributions

    1. You’re welcome. 🙂

    2. vdiv says:

      Ditto!

    3. SparkEV says:

      Tom is good, but why is it that many (most?) i3 drivers are courteous bunch? I had another encounter with i3 at DCFC where she disconnected before full free 30 minutes so I can charge. This happened several time before. This never happens with Leaf drivers.

      1. Tom Moloughney says:

        I can’t answer that. Kinda goes against the reputation that ICE BMW owners have, right?

        The one thing that I’ll say is there’s a very active I3 community on Facebook and some of the other forums. And this topic of being courteous at charging stations especially DC fast charge stations has been discussed many many times so perhaps it’s starting to sink in.

        1. vdiv says:

          The Electronauts have set the tone 🙂

  6. Ricardo Silva says:

    Excelent information and specially a honest analysis.
    I’ve a 2016 BEV and i’ve the same opinion about many factors that can affect available capacity, but at the end the battery capacity-loss will not be so significant.
    Congratulations!

  7. Warren says:

    I don’t expect most companies will be offering an upgraded battery for their older EVs. By next spring, we will have at least three “affordable” 200 mile range EVs. But I think the entire industry is desperate for the solid state battery to make EVs mainstream. I suspect sales of PHEV will outpace pure EVs until that happens.

    1. Warren says:

      Actually, companies may offer upgraded battery replacements, but at a price which will make trading it in on a new car more attractive.

      1. alohart says:

        Just like with NiMH battery packs for early hybrid vehicles, I expect 3rd-party replacement battery packs to be available for EV’s for substantially less than the price auto dealers will charge. For those of us who don’t want the expense of replacing our cars frequently and who are satisfied with our current EV’s, replacement or upgraded battery packs will likely be more affordable than replacing our EV’s.

        1. Warren says:

          I hope so. I would have expected to see something, by now, for the Leaf. Several individuals have talked about it, but no real products yet.

          1. Terawatt says:

            I too think this will eventually happen, but I didn’t expect it to happen now. EVs are thinly spread and the vast majority of them do the job. Relatively few will upgrade unless the price is very low, maybe as low as the cost of producing the battery…

            Test yourself. How much would you pay for a 50 kWh pack? What does it cost to make?

            Then consider that a garage needs to attract enough business to make it worth their while training people and buying equipment for a job that’s very different from what they usually do. Even if everyone else is as willing to pay as you are, how much room is there for any profit to be made? How certain is it that it will even be a profit?

            Remember that most of the EVs on the road were sold in the past three years. Not very many of them have suffered much degradation. Once the production cost, mark-up to the battery maker, markup to the garage and labour has been included, a replacement is still simply going to be too expensive to attract many buyers. And if they are few, the profits need to be juicy to make this a risk worth taking for any garage owner.

            1. Pushmi-Pullyu says:

              “Once the production cost, mark-up to the battery maker, markup to the garage and labour has been included, a replacement is still simply going to be too expensive to attract many buyers.”

              Right on target there, Terawatt. Battery packs are expensive for auto makers, and they would be even more expensive for the aftermarket industry, which would be making far fewer of them, and thus the aftermarket pack would have a significantly higher unit cost.

              I don’t see that happening unless the replacement pack can use significantly less expensive batteries. So it might be worthwhile if battery makers start making cheap, lightweight solid state plastic batteries. But it seems very unlikely that we’ll see the aftermarket industry offering 3rd party replacement battery packs using something similar to the type of li-ion batteries in use today.

  8. franky_b says:

    Thanks Tom, I don’t have as many miles as you, but this morning my i3 was showing a very up beat 93 miles of range, something I can do in city driving. I can do just over 80 miles on the highway. That’s after 2.5 years, 23K miles and over 150 DCFC recharge.

    http://sway.com/TqtvcLVrfRJLHNMV

  9. That’s good to hear, Franky. I also use DCQC frequently. I have a DC Fast charge station on my property so I can use it anytime. However it is one of the lower-powered DCQC stations and only charges at 24kW. However for the relatively small battery of the i3, it’s really all that’s necessary.

  10. vdiv says:

    Keeping the battery pack cool and staying away from the extremes of the charge window seem to be the key. Wonder if BMW will continue with direct refrigeration in the battery pack and if other EV makers will take that approach instead of glycol heating/cooling with a heat exchanger.

    At this point we have heard of more frequent failures in the power electronics and contactor relays than in the actual cells.

  11. Andreas says:

    Great article and research. I drive an i3 and this is encouraging to know. Even though it’s a sample of 1, we now know that it’s at least possible for the battery to perform on this degradation curve. If one excludes edge cases related to extreme weather I see no reason why this shouldn’t apply to most other i3s.

  12. bro1999 says:

    It’s actually misleading to say the Leaf even has air cooling. It only has passive air cooling, while vehicles such as the Ford C-Max Energi have active air cooling.

    Shame on Nissan for cutting corners with the initial MYs of the Leaf by ignoring the heat issue on hotter climates where they new early Leafs would “wilt”.

    1. bro1999 says:

      “ignoring the heat issue in hotter climates where they knew early Leafs would “wilt”.

    2. SparkEV says:

      I’m not so sure if they ignored it or just didn’t consider all use cases.

      Had Leaf been driven so that it’s charged when cool (at night) driven when cool (morning/evening) to 50% or less charge, parked under hot ambient without plugged in, and do this every single time, I’m not sure if you’d see so much degradation. Sure, it’d lot less usable, but the thought of “commute car” would conjure up this kind of scenario.

      Not sure if Bolt kicks in TMS without plugged in; SparkEV doesn’t. If it doesn’t, charging it to 100% then unplugging in hot temperature would degrade the battery quickly. Clueless dealers in Palm Springs / AZ who always charge EV to full before parking it under the hot sun unplugged are killing the battery.

      1. vdiv says:

        That’s weird as the first gen. Volt would continue cooling the battery even after unplugged.

        1. SparkEV says:

          I think Volt can afford to do so since gas engine is there, and it’s not so sensitive to battery use. But for BEV, using energy from the battery will eat range, especially small battery EV like SparkEV.

          If other BEV also do not cool when not plugged in, a general rule of thumb would be to buy EV that’s made in cool weather before hot weather starts (eg. made between Oct to Apr, bought before summer starts). That way, it’s not affected much by dealer treatment during summer. Worst would be to buy in fall something that was made in spring.

    3. Yes, we discuss that up in the thread. SparkEV mentioned the differences.

      It’s not always possible to explain every detail in articles like this. I also wanted to talk about how I frequently used DC Fast charge, and that there is some speculation that high speed charging may cause premature capacity loss, but that was cut for brevity also.

      1. Pushmi-Pullyu says:

        Tom, I really appreciate you taking the time and trouble to give us this detailed first-hand report. Even though it’s only 1 data point, I still find it quite valuable, as you’ve taken a deep dive into the issue of battery aging, and I see it has generated some really good discussion in comments.

        I know that InsideEVs prefers shorter articles, but I hope you’ll write another article or two to explore these other issues that you had to leave out of this one.

  13. Warren says:

    All the expense/complication of TMS will go away, if Goodenough is right. Only then will EVs become truly competitive with ICE.

    1. vdiv says:

      I had to climb a rather steep hill on a cobblestone road covered with sand and gravel in an old, stick shift, propane-converted SAAB 9000 today. I have never missed driving an EV so much. In my book not only EVs are “competitive” with fossils already, they are on another level.

      1. Warren says:

        Yeah. Me too. But handing out pamphlets on street corners isn’t going to convince most people. Only comparable, unsubsidized price, range, and vehicle life will convince people. We are not there yet. But if Goodenough is right, we won’t have to do any proselytizing.

    2. pjwood1 says:

      Wow Warren, a rather troll-like comment. To what are we comparing TMS complexity? Why not something that exists, like the cooling jacket of an internal combustion engine. I’m sure “Gasket Failure” rings a bell to a few. Have you got any good “puddle under my car” links, from all those inferior EV sites. Please, do share.

      1. Warren says:

        I am being “troll-like” by being honest? Why do you think Nissan gambled on their simple pack design? Why do you think the Obama administration put 120 million into the JCESR?

        1. pjwood1 says:

          Your words: “if Goodenough is right. Only then will EVs become truly competitive with ICE.”

          I began comparing the mechanical failings of combustion engine cooling, to cooling a lithium battery, and you point to the Leaf and Obama. Sounds evassive.

          I’ve pushed 5k lbs of Tesla inertia around enough to know how far up the performance curve you have to go with lithium ion before it begins cutting back (to ~300HP!). It has been ready for the street, for many years. Way better than a foolish reciprocating heat box.

          It’s amazing internal combustion engines aren’t dwindling faster. They will because they are not competitive. Simply not quick, or fast, in public.

          1. pjwood1 says:

            ..evasive

        2. Pushmi-Pullyu says:

          “Why do you think Nissan gambled on their simple pack design?”

          I don’t know; looks like they decided to go the cheap route. Didn’t work for them, did it?

          At any rate, your comment makes no sense. If tomorrow someone invents a battery that has a wider range of operating temperatures — will the plastic solid state battery have that property? — then we can pretty much forget about complex expensive battery pack thermal management systems.

          1. Warren says:

            I’m not talking about the polymer electrolyte/separator solid state batteries. I am talking about Goodenough’s glass electrolyte/separator battery.

            Yes, Nissan decided to go the cheap route, because the batteries are too expensive.

            We will be buying a Bolt based on ethical concerns about funding terrorism, and planetary destruction. But not everyone has that luxury.

            If you want to see the market value of current EVs, look at AutoTrader. New “affordable” EVs, in the US’s largest car market, are going for 50% off list! We can argue until the cows come home. By next spring we won’t have to speculate about whether EV’s, with current battery tech, are competitive in the mass market. I hope I am proven wrong.

            1. Warren says:

              These prices include state and federal incentives. But again, not everyone can take advantage of them.

  14. Terawatt says:

    There is one issue that’s somewhat glossed over in the article: individual batteries do vary considerably both in actual capacity and how they degrade over time. See a few YouTube videos with guys doing DIY e-bikes, and you’ll quickly note how many of them order more 18650 cells than they intend to use, test each of them, and throw out the bad ones. Auto makers don’t do that, and for small-cell packs like Tesla’s it would add significantly to the time and thus cost to do so.

    Hopefully as more data becomes available the manufacturers will give better warranties. 8 years and 100k miles is maybe enough, but 70% is a bit low. If less than a percent of the packs fail to meet stricter standards, say 80% in 10 years and 150k miles, I’m sure buyers will prefer to pay 0.5% more for the car (the battery being less than half the total cost, after all) and have the extra security rather than run a small but real risk of getting a lemon.

    Tesla in particular could do much more to ensure individual customers won’t find themselves in a crises because of bad luck. Their batteries perform excellently by all accounts, but their battery warranty doesn’t guarantee ANY minimum capacity – only a lifetime without failing completely. But precisely because their packs appear to be such solid performers, one would think it would cost Tesla very little to give customers a solid capacity promise. They’ve got enough data to know pretty well how many packs will need replacement under warranty for any given level of guaranteed remaining capacity. The only difficulty I see with this is that Tesla then assumes the risk when it makes innovative changes to its battery tech – but that’s clearly fair! Customers can’t reasonably judge this, and should get something more solid than Tesla’s reputation for (mostly) great customer service to rely on.

    1. Pushmi-Pullyu says:

      If you think each and every cell going into a Tesla battery pack isn’t tested before it’s put into the pack, then think again. I dunno if Tesla pays Panasonic to test them before shipping, weeding out the rejects which show slightly higher or lower voltage, or if Tesla does that in-house.

      Just read an article about someone who has disassembled a Tesla battery pack, and see how they comment about how very nearly all the cells are perfectly balanced in voltage, with only the rare dud which has failed during usage.

      It’s hardly a surprise that DIY battery pack builders need to do their own battery cell testing when assembling li-ion packs. The places they buy cheap li-ion cells, such as ebay or an overstock merchandise vendor, certainly can’t be depended on for quality control. A lot of those batteries are going to be factory seconds, or returns which the battery maker can’t sell as new. Buying from those sources is a mixed bag. Sometimes you might get lucky and get a good, well-balanced batch all exactly alike. Other times you won’t be so lucky; there might be cells from different companies and/or with different chemistries.

  15. ModernMarvelFan says:

    Just another example to confirm the importance of liquid cooling…

    1. SparkEV says:

      i3 doesn’t use liquid cooling.

      If you mean active refrigerant based cooling, be it gas like i3 or chilled air like SoulEV/iMiev or liquid like SparkEV and the rest other than Leaf and eGolf, yes, active refrigerant based cooling is essential in EV.

      1. Pushmi-Pullyu says:

        Okay, make that “active fluid cooling”.

        But the most important point here is that Nissan with the Leaf (and, I guess, Mitsubishi with the iMiEV) depended on passive cooling. No fluid is circulated through the pack; not a water-based liquid, not a refrigerant, not even a fan to provide forced air flow.

        In other words, no way to stop excess heat from building up inside the pack, or to cool the pack down quickly if and when that happens.

        We see the result in a lot of Leafs with pack capacity loss significantly higher than can be explained by normal usage. We see none of that in packs with active cooling, except where there has been a malfunction.

        The difference is pretty stark.

      2. ModernMarvelFan says:

        “i3 doesn’t use liquid cooling.

        If you mean active refrigerant based cooling”

        Is the refrigerant a form of liquid when it was in the cooling state to absorb heat from the battery?

        Yes, it becomes air or goes thru phase change to release the heat to outside…

        Either way, the “liquid cooling” was aimed at the fact that on the boundary of battery, the liquid whether it is coolant or refrigerant contains far more cooling capacity so heat can be properly removed.

  16. George B says:

    Great data and article, Tom! Kudos for gathering so much useful data. Dave Murray came up with a nice video explaining why we see some variability in battery capacity and how the battery controller adjusts its estimates based on continuous use and operation of the system.

    Dave has been driving plug-in vehicles for several years and this video is a great introduction to concepts that apply to automotive battery packs as well. BTW the “Batt.Kapa.Max” is an abbreviation of the German expression “Maximale Batteriekapazität”, which is pretty self-explanatory.

  17. Jonathan Brusco says:

    I’m going to begin by stating that I’m by no way defending the Leaf as a great example of battery longevity, but there’s some details that need to be pointed out here regarding the battery tech in the i3 and the Volt. Yes, both have different cooling and TMS, which will help them hold up better over time, but all of the comparisons regarding loss, have to do with usable range of the cars not on actual degradation. There is a difference.

    To start with the Volt, it sets aside a large amount of the battery capacity as “unusable” and only makes about 70% accessible to the driver. This means that the pack never operates at or near it’s highest charge, therefore it maintains lower temps and less stress on the pack. It also means that the software in the pack can identify the degradation and eat away at the unused capacity over time without impacting the usable range that the driver experiences. The pack may feel like it hasn’t lost capacity, but in fact you’re simply not experiencing it as the driver.

    The i3 also sets aside a much greater amount of it’s pack in reserve compared to the Leaf. It has 18.8kwh usable capacity compared to the 22kwh of the full pack. Compare this to the 22.6kwh usable capacity of the Leaf’s 24kwh pack and you’ll see what I mean. The i3 is about double that of the Leaf. The referenced owner in the article said that he lost .8kwh of capacity. This may be true, but it also cold mean that he’s experienced only the equivalent of .8kwh of loss because other degradation was absorbed by the unused part of the pack.

    Ok, so why should we care? I’d say that while the Leaf gets most criticized for it’s range loss, and rightfully so, the 2011/12 cars were very very bad, their loss is somewhat exaggerated by the increased amount of usable pack capacity, whereas on the Volt and i3, you’re not really sure where you stand on the degradation based on the unknown usage formulas for the cars. Sure, the Volt/i3 methods are a better user experience for the owners, but this too may not remain forever. If indeed the car is eating into the unused capacity, once doing so is no longer possible, it will begin to eat away at the usable capacity with much greater speed and the owner may experience far greater degradation rates over time.

    1. There’s truth to that, Jonathan. The one thing it’s say though, is that most customers are mainly concerned with how far the car can go when new, and how much less it can go after x# of miles or time. So in that regard, this kind of measurement is a good metric.

      Also, the i3 has a 21.6 kWh pack, and I used 19 kWh for my baseline starting point, so that tightens it up a little. I do agree the Volt absolutely uses the pack differently than the LEAF or i3, and holds a much larger buffer. But from the customers point of view, they aren’t experiencing any loss of range so they are happy.

      1. Jonathan Brusco says:

        True that the extra capacity to eat away at does provide a better user experience, but we will soon see what happens as these early cars get to 120K+ miles and there’s no added capacity to eat into. I know that in the Leaf the packs that approach end of life see a drastic drop in range, not only due to the degradation, but also due to the fact that they can’t regen as effectively. These two factors combined make a much larger dent into the usable range. This will be much exacerbated as the i3 and Volt degrade as well. I do like that the i3 has their pack divided into 8 different sets of cells. I wonder if they utilize them in a formula that leads to even degradation or if they specifically set it up so that a replacement of a few of them will breathe a lot of new life into the pack?

        Lots of what ifs here. What I’ve learned as an EV driver and owner is that my next car (likely a Model 3) will be purchased with the largest pack option. With the ability to cycle through less frequently and have increased range to utilize, I’ll hopefully be able to get 250k+ of miles out of the pack before feeling a serious dent in range that will impact me lifestyle.

    2. cab says:

      Is there an “OBD II accessible” parameter for the Volt’s ACTUAL capacity? That could tell the tale. Like others, after 3 years/34K miles on my gen 1 Volt, I had a hard time telling if it had lost any real range. Day to day driving was variable enough to make it difficult to detect.

      At the end of the lease, I do remember thinking I felt like I was down “about a mile” – not scientific for sure, but also telling of a “no big deal” experience.

      1. Pushmi-Pullyu says:

        I doubt the data is accessible by anyone without using GM’s proprietary software. If there was, there wouldn’t be so much argument over how much or how little capacity Voltec reserves in the battery pack to prevent degradation from showing.

  18. Pushmi-Pullyu says:

    “Obviously that the rate of 2.3 miles of loss per 10,000 will likely accelerate at some point, because battery capacity loss isn’t linear…”

    BZZZZT! Wrong, but thanks for playing!

    Actually, on average the loss of capacity slows slightly over time. As I understand it, that’s because the physics of the situation works so that any loss of capacity due to cycling is a percentage of remaining capacity, not full capacity.

    1. Carsten says:

      There are 2 apps for the MiEV, that monitor battery health and other stats: Canion and evbatmon.
      I use cCanion with a BT OBD2-device.
      There should be similar apps available for other EVs.
      It would be nice to know, so that I could go into the dealership and check the battery health of a used EV prior to purchase.

  19. EvMan says:

    Cost of ownership.
    What ever money u will save with the i3 battery , the damage prone, expensive and low life tires will eat away. The rest will be taken care by the BMW reliability.
    When i read about the complexity of the Volts hybrid terrain (3 mode in gen 1 and 5 mode in gen 2 ) , i was so surprised, that the BMW Rex is so simple ( only serial) , and still manages to get so many drive train errors.

    1. WARREN says:

      What?? I race my i3 all the time, had 18000 miles on the tires. As much as any of the gas cars I have owned. Driving the same way, I wore out my LEAF tires in less than 8000 miles. The BOLT tires wouldn’t get my 5000 miles I bet.

  20. Null says:

    Little discussed, Nissan seems to be playing shameful warranty games. There are reports of not enough bars lost to trigger warranty replacement, but with less then 1/2 the useful range.

    Great way wreck your brand!

  21. James says:

    Notice, no mention of Ford as our poor Energi have poor battery thermal management. The Focus at least has liquid cooling so may fare better.