Op-Ed: To SOC or not to SOC – The Future Is Here And It Is Called The BMW i3 Range Assistant

DEC 10 2013 BY DSCHURIG 74

BMW i3 Outdoor Test Drives At LA Auto Show In November

BMW i3 Outdoor Test Drives At LA Auto Show In November

There has been much discussion on the boards recently about BMW not including a State Of Charge(SOC) indicator in the new i3 for the United States model.  Many veteran electric vehicle(EV) drivers have expressed major disappointment, their EVs have always had SOCs, some owners going so far as to retrofit third party meters on vehicles not so equipped.

Why would BMW make such a strategic mistake omitting a gauge that is so vital for daily EV use? It is true, SOC is a commonly found indicator on board EVs of all kinds and drivers have come to rely on them heavily to know their range among other things. But how necessary is it on the BMW i3?

Editor’s Note:  Our thanks to contributor Darren Schurig (Yiiikes) for putting to together this op-ed

What is it that we really want to know?

  1. Are we going to make it to our next destination?

  2. How far can we go before we need to recharge?

The two critical pieces of information that have created a frenzy of apprehension about EV transportation and engendered use of the expression “range anxiety” due to the lack of a gasoline-like recharging infrastructure. The term first surfaced during the era of the GM EV1. GM went so far as to file for a trademark on the term presumably to use as part of their new plug-in hybrid marketing campaign (their filing was not granted). Much like a fuel gauge in an Internal Combustion Engine(ICE), the SOC is the primary meter used to answer these questions.

The Venerable Dipstick

Early gasoline automobiles did not have fuel gauges, in fact they did not have any instrumentation, the technology did not exist. Fuel level was measured with a dipstick that was inserted into the tank. A dipstick could be calibrated to the shape and volume of the tank or merely measure inches of fuel. The first dash-mounted gas gauge for an automobile was by Studebaker in 1914. Rickenbacker offered the first electrical fuel gauge in 19251. It provided real time information and was more convenient – it was better. Ultimately the automotive fuel dipstick went the way of the dinosaurs. It is still in use today however for light aircraft, industrial applications and more.

The Dipstick

The Dipstick

What is SOC and how do we use it?

SOC in its most rudimentary form is a measure of the amount of energy stored in a battery just like a fuel gauge tells us how much gas(energy) is left(stored) in our tank. As a metric, it does not directly answer either of the two questions above. Analogous to the fuel gauge of the (ICE) vehicle, we must take it as a starting point to a long series of considerations, all the things that affect how fast the stored energy(fuel) will be depleted – distance, road type, elevation changes and driving style. Using a combination of guesstimates, hunches and intuition as an “algorithm” in our head (try writing it down someday) that we each develop ourselves for our particular EV, we determine the answers to the critical questions above – in the same way we would for an ICE vehicle on a long trip (rarely necessary in urban area trips due to the extensive gasoline refueling infrastructure). In that way, an SOC is a holdover from ICE technology.



GM EV1 Readout

GM EV1 Readout  – 3

The GM EV-1 had an SOC gauge in 1996, 18 years ago.  It looked exactly like a digital ICE fuel gauge of the GM products at the time (see fig. 3.6). That was the technology of the day, nothing else existed to aid in the understanding of your energy use profile. But does an EV need to merely be an electric analog of the ICE that has massively overshadowed it all of these years?

The World Changed

The global technology that has been created in the last thirty years is positively transformational. We quite literally could not maintain our daily lives today without most if not all of it.

  • Computers-small machines that can reliably perform an unfathomable number of calculations or instructions in the blink of an eye
  • Artificial Intelligence-machine learning through regression analysis, decision tree learning, association rule learning etc.
  • Cellular Phones –wireless communication with wide geographic coverage
  • The Internet/World Wide Web-publically accessible repository of every kind of media and information imaginable
  • Global Positioning System (GPS)-a system of satellites and a receiver that can pinpoint our position and elevation on the globe to within 7.8 meters (accuracy of better than 3 meters is possible)3
  • Web Mapping Services (Google Maps) – extremely accurate mapping of the physical world with visual imagery of virtually the entire globe. Includes route planning with distance and time to destination
  • Real Time Traffic Services (Traffic.com)-provider of traffic information via a number of media, including the Internet, cell phones, radio, satellite radio and television in the United States
  • Mobile Web– access to the World Wide Web from a handheld mobile device over the cellular network
  • Smart Automobiles-dozens to hundreds of on board sensors and processors to monitor vehicle conditions and enhance safety and performance – wheel speed, ambient temperature, cabin temperature,  engine temperature, accelerator position, yaw, roll, acceleration, steering wheel position, parking (proximity), blind spot , tire pressure,  ad infinitum

As an example of how these developments have become indispensible in our lives because they are so much better than the technology they replaced, Goggle Maps makes it possible to know the route, distance and elapsed time to any place in the US in a couple of seconds. And it is accurate to within a tenth of a mile (528 ft). That is substantially faster and far more accurate than paper maps or Thomas Guide or any kind of estimate we could do in our head.

What if . . .

…you could combine all of these remarkable tools, each one life-changing in and of itself, into one solution that could tell you precisely how far you will go with the energy you have on board? And what if it was continuously updated in real time? And presented in a simple to read color graphic? Unimaginable?

Well it is here today and it is called the BMW i3 Range Assistant, the most advanced and sophisticated ranging utility ever developed for a consumer product. Much like the automobile that subsumes it, it is an ingenious combination of the technology that has vastly enhanced and shaped our lives in the last 30 years.

BMW Range Via Different Modes

BMW Range Via Different Modes

Incorporating all of the technology above, it evaluates battery charge level, driving style, use of electric convenience systems (heating/air conditioning) choice of drive mode, route topography (inclines and declines) and the current traffic situation and generates a very simple to understand map visual on a mini tablet sized display that directly without any interpolation answers the two questions above. It displays the radius of range for each of the three drive modes and clearly indicates whether you will reach your destination or not. You don’t even have to tell it where you want to go. Notice that the range radii are not circles – Range Assistant iterates possible routes from your current position and corrects for range sapping or supplementing  factors for each.  If your destination is in the shaded area, you will get there, it is that simple.

This information is shown on the dynamic range display in real time which provides an overview of all possible destinations. If a destination is out of reach, the car will suggest going into ECO PRO or ECO PRO+ mode to maximize the vehicle’s range by limiting the top speed and switching the heating / ventilation system into an energy-saving mode. If that still isn’t enough, the car can display public charging stations in the area which can be reserved from the display. A casual glance at the display and you know precisely and directly the answers to the two critical questions. It determines range using more data points, more precise data, and orders of magnitude more accurate calculations than anything we can do in our heads. No guesstimates, no hunches no mystical algorithm. And no range anxiety.

BMW i3 Heads-Up Display On Charging Locations

BMW i3 Heads-Up Display On Charging Locations

Like the fuel dipstick that was displaced by the better fuel gauge and the paper maps outdated by Google Maps, gone is the tiny seven segment display of esti-mated range and the need for SOC. SOC is as necessary to a BMW i3 with Range Assistant as a fuel dipstick is to a new 535i – obsolete technology.

Technology Realized

In 1986, I was on a team in college that designed and built a carbon fiber reinforced polymer(CFRP) monocoque with aluminum component Human Powered Vehicle(HPV), very possibly the first of its kind (pre-preg carbon fiber was $4,000 a lb. at the time). It was utterly beyond our young engineering intuition how a material could be so light and so strong. We second guessed our analysis many times before building it out and competing with it.

Years later I worked for one of the world’s most renowned automotive concept and prototype fabricators and in 1998 we built the first carbon fiber monocoque on aluminum chassis concept car for one of our OEM customers. Again the strength to weight property of the material was mind bending. We went on to build many more that included fuel cell, electric and hybrid drivetrains. It was obvious to us at the time that CFRP would find a place in automotive manufacturing once the problem of mass-productionizing it could be solved. Incidentally several of the designs we built had “coach” or suicide rear doors.

Now 15 years later BMW has made that future a reality for mass production and with it introduced a new transportation paradigm on every level. It is the first automobile I have been excited about since my 2002 BMW M3 and those CFRP on aluminum concepts we built. It ushers in a truly new way to engage in transportation, a culmination of technology and sustainability never before seen.

A Truly New Paradigm

Electric vehicles span a full range of designs from ICE platforms that have been modified in one way or another to accommodate electric drivetrains to purpose built, clean sheet designs that truly leverage the unique opportunities presented by electro-motive drive. Tesla Model S is a great example of a clean sheet design with amazing reliability, luxury and performance. Even it is still an industry standard automobile in its appearance, material and construction, albeit a remarkably good one. Several of my friends/colleagues that worked with me on those original CFRP concept vehicles are engineers at the Tesla engineering studio.

The BMW i3 is truly a new paradigm in automotive language, a clean sheet design that leverages new visual language inside and out and employs new materials and construction that sets a new bar for architecture and weight management. The EV no longer needs to be a copy of an ICE with an electric motor.

Going hand in hand with that paradigm shift is the most accurate and reliable range prediction utility ever made available to the public. It answers very directly the two questions that opened this editorial with a casual glance that can be understood by anybody. No more interpolating and guesstimating and hunching your way to your next destination. A human can never hope to be able to know or account for the fantastic volume of data the Range Assistant incorporates into its prediction, let alone approach the accuracy of its calculation.

Thank you BMW for bringing such a remarkable vehicle to our world. Early adopters unite, embrace the new paradigm in all of its glory including the i3 Range Assistant. Allow an EV to be something completely different than an ICE and bury your need for an SOC with the fuel dipsticks and Thomas Guides!

One final note, another question that an SOC may be useful to help answer – How long will it take to recharge the battery from its current level to full or any other level? BMW i3 has a solution for that too . . .

BMW i3 App

BMW i3 App

Darren Schurig (Yiiikes)

  1. History of the Fuel Gauge, http://www.crankshift.com/fuel-gauge/

Measuring Fuel in Early Fords, http://www.post-journal.com/page/content.detail/id/608693/Measuring-Fuel-In-Early-Fords.html

  1. How does GM’s fabled EV1 stack up against the current crop of electrics?, http://www.digitaltrends.com/cars/how-does-gms-fabled-ev1-stack-up-against-the-current-crop-of-electrics/

  2. Performance Characterization, GM EV1 – Southern California Edison, pg. 6

  3. www.gps.gov

Categories: BMW


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74 Comments on "Op-Ed: To SOC or not to SOC – The Future Is Here And It Is Called The BMW i3 Range Assistant"

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I still want a SOC meter, sorry.

Can somebody edit an old “I want my MTV” clip to say “I want my SOC”!

SoC is just a range indicator in most EVs, anyway, right? So, it’s doing a lot of questionable calculation and guessing for you already! What you really want is a pretty dead-on measure of the number of usable MegaJoules or kWh accessible in the battery.

Or, just the raw voltage I guess.

I’m really glad that ECU’s were forced to open up their data 2 decades ago and we can always access more-raw data–like voltage and usable MJ/kWh in the battery–with a bluetooth adapter and a tablet when we want to. Heck, I leave my OBDII adapter connected and keep one old phone in my car on the dash just for viewing ECU data, no special occasion needed.

What I really want to know is how many kWh are in the battery. SOC is already one iteration away from kWh, anchored by usable capacity, which can vary by age and temperature. Miles remaining adds several additional variables, so is even farther from a useful value. To be truly predictive the miles remaining indicator must know destination, route, elevation, and weather. And it must control HVAC, speed, and acceleration/deceleration. When cars drive themselves, I’ll believe range remaining. In the interim, I’ll have SOC please.

Not really, SOC and energy remaining are at about the same level of abstraction from measurable things in the battery. I know of at least one major battery manufacturer that derives the energy remaining in kWh from the SOC. There is no magic way to measure the energy content in a battery, all you have is the voltage of the battery, the history of the current going in or out of it, and the characteristics of the battery, characteristics that may in fact change over time. The battery guys have their tables of open circuit voltage vs SOC, internal resistance, capacitive effects, they look at the voltage of the battery, maybe do some integration on the current, and calculate a number that’s useful to the user. Whether they express that in SOC (% of total energy capacity) or kWh is pretty much telling you the same thing, no difference in the factors that go into the calculation. If you were brave you’d ask them to give you a voltmeter and an ammeter like some of the more crude DIY EVs out there!

Same here, KeiJidosha, I would really want to see the kWh figure exposed somewhere. The Renault Fluence does it, and it can be done. LeafSpy from Jim Pollock does it on the LEAF, and several of us provided extensive input and suggestions to him. LeafSpy has been adopted by hundreds of LEAF owners, including experienced and pragmatic folks such as Nikki Gordon-Bloomfield. That said, we had this discussion with Mr. Schurig in the comments section on the article Tom wrote. While I appreciate his efforts and time to express his thoughts on the matter in such a detailed and compelling way, I disagree with his portrayal of “a frenzy of apprehension” among “veteran electric vehicle drivers”. Perhaps I’m misreading this, but this seems to lead readers into believing that peerhaps some hardcore old EV drivers don’t want to see the Range Assistant for what it is, don’t appreciate its awesomeness, and somehow fail to migrate away from their ancient habits and methods, while insisting on anachronisms such as an SOC meter being included in this cool new EV. This couldn’t be farther from the truth, and I would contend that Mr. Schurig seems to compensate with rhetoric and conviction what… Read more »

Doesn’t the I3 tell you how many miles you have left of range and the percent battery remaining? That’s all you really need…


No it doesn’t. I’ts the percent of bettery remaining that is missing.

And yes, we want it! It takes a minute to implement it and another minute to push it out over the air as an update for the i3 (assuming that is how they update, but surely they do…anything else would be an epic fail nowadays).

Written like a true tech nerd. Get your head out of the cloud. With the crumbling infrastructure here, the power goes out when it rains, like it did for several hours on Saturday! In short order the cell towers stop working. Just give us a damned SOC meter.

This is why God gave us OBDII and cheap android smartphones to view the data with, man.

Yes, but someone has to do the CAN bus hacking and design an app for that. This was a lot of work on the LEAF, for example, because the manufacturer did not share any information with the drivers working on this. A SOC percentage meter is easily included for the OEM, but it will require an inordinate effort on the part of volunteer hackers, not to mention a semi-permanently OBDII dongle lodged in the diagnostic port.

This whole article could have been replaced by a sentence.

“Yes we want one and need one, implement it now!”

Well thought out and written, but basically what you are saying is you (or BMW) knows what’s best for me. That’s not how it works. It’s the customers choice, and the manufacturers job to make the customer happy. Give the people what they want, and the vast, overwhelming of people that have previously or are currently driven electric cars want to see their state of charge displayed in a numeric form.

Yes, they want other info like what the range assistant will provide. They also want real time energy usage and cumulative energy consumption data. Just give them everything and let them decide what they want to look at. Some will look at the range estimator and some will look at SOC, who cares as long as they are happy?

Tom, I think you have made some great points, I just am not sure the majority agrees with you on SOC. The gamers among us (me included) like the stats and hence want the dang SOC meter.
I think the early adopters want this.. but the other 98% of the population doesn’t care. My grandpa always said, “I just want comfort and reliability, that way I can get from point A to point B without having to think about the car.” Ironically, I think he hated the range-o-meter in his Lincoln and instead prefered the gas gauge.
So, that leads me to believe BMW has made a mistake here, alienating the early comers and possibly the driving enthusiasts they are trying to attract. As you say, “why not just put it in there?” You have nothing to lose.

Cody, this is not true. I spent vast amounts of time supporting hardcore technically versed early adopters on the forums, and much more casual users on Facebook. The percentage SOC meter is something that’s simple and most people get instantly. It provides valuable additional context and information. Most folks are used to this metaphor, since they see it on their laptops, mobile phones, music players, etc. This is not limited to automotive, and the comparison with a fuel gauge and the dipstick is deliberately misleading, and that you are missing the point of all this.

This article reads like an ad for BMW. In any case, can’t we have the Range Assistant AND an SOC meter?

It is strange that the article ends by saying BMW has a way to tell you how long it will take for the battery to change “to a certain level”. But… why not just apply the Range Assistant here as well? — that is, just show me how long I will need to charge in order to make it to point X. Show it as a map with concentric rings of charge time.

This is no longer about the SOC. This is about BMW’s intention to listen to their customers and respond to what they need. Not doing so is a good way to lose current and potential customers.

Does the i in the i3 stand for idiots? It is good to know if that is how BMW feels about their EV customers.

I think I have said enough on the matter.

Maybe I read this too quickly and missed it. But it is one thing to know you can make it to this store and that… But can I get to that store and THEN have enough juice to make it home? Also this seems like a geek thing. My wife doesn’t do maps or judge distance. So I just told her to stick it in Eco mode and make sure her next stop is home if it ever shows 20%. She has been fine with that. -1 for the car that doesn’t have SOC.

This is great point. Not every judgement about “remaining range” has to do with only making to some “one” next destination that is within range of a certain driving style (what the Range Assistance seems to show best). You may have several stops planned, some of which backtrack within your driving area, etc.. It doesn’t seem that the Range Assistant’s display can help visualize this.

Right now SOC is worthy of debate. With the arrival of “The Better Battery” one only needs to charge at night and worry about range when on a distant trip. I’m looking forward to the good times when Nissan drops the Fuel Bars, Estimated Range Calculations, Driving Efficient Dots and those damn Growing Trees on the Leaf.
Link to the best chance for the Better Battery: http://www.youtube.com/watch?v=PEHs3X75IDo

Looking at my iPhone and iPad, each with a SoC indicator in the top right corner of the screen. If every modern cell phone has a SoC indicator, wondering why it is to difficult to have one in an electric vehicle.

btw: current status: 64%

The Renault Zoe does have a kind of SoC indicator but it’s just a graphic that looks like the kind of thing you get on a cell phone. There’s no kWh or % displayed. Instead, there’s the Zoe’s estimation of available remaining range based on your recent driving style. Other than the pretty map of where you can reach (which you can get on the Zoe if you choose it from the TomTom nav – but I rarely bother) I don’t see any difference between this and the i3. Personally, I prefer a number in miles because then I can easily estimate a multi-stop trip. If you *really* want to, you can try to work out the battery level graphic – depending on your driving style each of the 8 segments is about 10 miles but the level goes down 1 pixel at a time, not 1 segment at a time. Originally I was surprised at a lack of kWh or % battery info but, you know, I’ve realised it just isn’t useful information. In fact, I’m really not that bothered about the battery graphic either and in all honesty I’d say seeing the battery graphic almost empty was more… Read more »

It’s not like its a fixed display like the EV1 shown above.
It’s an LCD screen, drawn by a computer. This computer has many more variables than we will ever see in the GUI

There’s no technical reason why we CAN’T have it, so just give us the option. By default it can be whatever the manufacturer “thinks is best”, but bury it in menus somewhere to customize the screen how I want it. After all, I’m the one paying for it, and I’M the one using it day in, day out. Not the marketing people, ‘customer experience’ people, or engineers. Me.

the BMW site gives you a ‘fixed display’ ‘range ring’ that they let you overlay on your location. given modern computing, I don’t know why all EV don’t have something like this:


This is all I need in a car’s user interface: good OBDII definitions and a good place on the dash to put a cheap used phone or tablet. Good and plenty open data, that’s my only requirement!

I’m totally with Yiiikes on this. SOC is a geek thing, if you ask the majority of people what a kWh is, they would return a blank stare (I work in Utilities and many people I work with have no idea), so getting them to convert that to miles is foolish.
What the BMW system also does, is allow them to build any type of car/SUV with any size of battery, and any range and have drivers immediately be able to feel comfortable and drive. With a SOC, you’d need to learn how efficient the vehicle is, how it changes with more occupants, wind, groceries and each vehicle would be different. This technology lets the vehicle tell you what its got left in the tank, in a way that you and particularly the average driver will understand.
The next generation is less and less interested in the workings of vehicles, they just want to know, “will it get me to x”, and this does it without having to know anything about the vehicle or the journey being made.

I disagree with the POV. Most consumer devices have a percentage SOC meter for their batteries. The laptop I’m typing this comment on has one too. I have never heard anyone complain about it and ask for a better graphical representation of the battery state of charge. Have you?

The article makes a good point that most of the time we’re interested in “distance” related questions and that BMW is providing one of the most advanced UIs to provide simple and understandable info.

However there are “Other” non-distance related questions that are better answered with SoC.

“How much capacity has my battery lost since I bought the car?”
“How much capacity is left in the used EV I’m considering buying?”
“I know it’s going to be much colder for the return trip tomorrow and I want to make my own milage estimate.”

So while the BMW UI is very nice, they should ALSO provide the SoC info, at least in a secondary screen. A gasoline tank will always hold the same 15 gals, but an EV’s “full tank” will be affected by age, temp and charging history. So an EV still needs the dip-stick equivalent of raw fuel capacity provided by SoC.

Yes, Joe, for this a kWh of usable or total capacity, either one, would be perfect. Unfortunately, most manufacturers opt out of this type of gauge. The argument we have heard was that “kWh” might sound too technical and too strange for a new EV driver. While the car buying public is used to such terms as “gallons” or “miles per gallon”, terminology related to electricity might sound too strange and off-putting. A percentage SOC meter is about as far as most seem to want to venture. I think the author of this article has a point, when he says that there is a limit to the type of technical information, which should be exposed to the casual driver and user of an EV. There is no reason why this type of data, including a percentage of degradation or perhaps percentage of original battery capacity remaining, could not be included in a sub-menu or some other not readily visible part of the car UI. Call it the expert screen, if you will. Thankfully, all of this information is already on the CAN bus, and all it takes is visualizing it and exposing it to the driver. It’s really an easy… Read more »

+1 for Joe.
-1 for the EV that does not have SOC.