Chevy Bolt Winter Fast Charging: Cold Versus Warm Battery: Video

JAN 23 2019 BY MARK KANE 58

Keep the battery warm if you want to fast charge in the winter

One of the Chevrolet Bolt EV users – Ste – tested the fast charging capabilities of the car at 28°F (-2°C) and shared thoughts on how to not waste time and money at the DC fast chargers.

The bottom line is that the lithium-ion batteries’ charging power (which translates to speed) is limited by temperature. From around 0°C typically there is a significant slowdown – the colder the battery is, the slower it will charge. The slowdown can be higher than an order of magnitude – for example, you might take on just a few kW instead 50-100 kW – at least until the battery warms up.

In the case of Ste’s Chevrolet Bolt EV, the deeply discharged and cold battery was able to accept less than 15 kW from a 50 kW EVgo charger, which triples the time and expense (if charging fee is by minutes).

The charging hardly exceed 15 kW after 10 minutes, and then slowly increased to 20 kW after 25 minutes. The last 15-20 minutes brought charging to over 30 kW as the battery has warmed to levels that permit a faster charge rate.

After some 45 minutes of charging, only 17.1 kWh was dispensed.

“As winter arrives and freezing temperatures settle in on large parts of North America, it’s important to understand that a cold battery significantly impacts range and charge rate.

The latter might not be as familiar to new electric vehicle owners, which is why I ran through this example winter charging session on my Chevy Bolt EV to show what you can expect.

Time Stamps:

1:08 – Location
1:30 – Three EVs / Two EV spaces
2:12 – Start of Charge / Lame Rate
9:50 – The Slow Crawl to Medium Speed
12:52 – Finally Getting Warm
14:15 – 45 Minute Auto-shutoff + Review
16:14 – Finishing Up + Planning Moan

Other models may fare better, but the key takeaway is to do what you can to keep your battery warm in winter, or at least warm it up before you waste time and money on elongated DCFC sessions. My intention is to also test whether a short period on a (free/cheaper) level 2 charger before hitting the more expensive DCFC would help expedite the battery warming process, but that will have to wait for another session when we have similar temperatures.

Also a sidebar to electric vehicle charging planners: try to include at least as many EV-only spaces as you have charging units!”

In the second test (see video below), when the battery was warmed up after driving, 17.4 kWh was dispensed in just 23 minutes, which is twice as fast and could be half as cheap.

The side effect of charging with a warm battery is it’s quicker, so the station can serve more customers.

“Following a frankly painful first winter charging test session with a cold Bolt EV battery, here’s our second attempt at similar ambient temperatures but with the vehicle battery warmed up after driving.

The results are immediate and obvious, but still provide food for thought to new EV owners. Time Stamps:

1:20 – Pulling in (Ghost Mall)
1:47 – Pre-charge recap
2:10 – Starting a charge session on EVgo
3:10 – Charge starts up
4:20 – Charge in progress/Dash close-up
6:40 – 10 minutes elapsed + session comparison
7:26 – Discussing EVgo rates + why you need a plan
8:55 – Discussing how to price out a charge session
11:28 – 20 minutes elapsed + session forecast
13:48 – Target reached + charge stopped: Summary
14:30 – Heading out + pondering Electrify America installations next to existing EVgo mall locations

If this is your first winter with a Chevrolet Bolt EV or any other electric vehicle, do what you can to warm the battery before attempting a fast charge session. That typically means driving at highway speeds for an prolonged period of time, but I’ll be researching/testing other potential approaches in the weeks ahead… the more you know!”

Categories: Charging, Chevrolet, Videos

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58 Comments on "Chevy Bolt Winter Fast Charging: Cold Versus Warm Battery: Video"

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Yep, the Bolt won’t unleash “full speed” (125+ amp) charging until the HV battery temp is between 70-75F. As the temp approaches 70-75F, the charging speed slowly ramps up to full speed. For example, if your Bolt’s battery was only at 55F when you plugged into a DCFC, your max charging speed may be between 30-35 kW (80-100 amps). The battery heater only seems to come on while unplugged if the HV battery drops towards 30F.
I’ve found that driving over 70 mph on the highway, even in the freezing cold, will warm up the HV battery temp. So if you have electrons to spare, the extra electrons spent driving faster as you approach the DCFC may actually save you a lot of time once you plug in.

Now that’d be interesting to see – a 3 axis graph of charging speed, battery temperature, and state of charge. I imagine there’s a nice sweet spot to maximize the charging rate – i.e.: warm battery at 10% state of charge.

Looking at Nyland video, Leaf battery warms up about 30C above ambient when driven for about an hour at about 90 kph (about 55 MPH). Bolt battery is heavier and Bolt is more efficient than Leaf, but even driving at 55 MPH would bring the temperature to toasty levels in time at freezing temperature.

My 2011 LEAF never approached advertised charge rates on DCFC. I live in a cool, but not cold place. DCFC was an almost useless feature for that car. Super expensive, not very fast.

I had my first DCFC on my 2016 LEAF last Saturday. This was a shiny new Electrify America station. Ambient temps were about 20F, SOC was 10% and I charged at 40-45kw from the very start. My leafspy screenshot doesn’t show battery temp at the start of charge, but when I stopped at 50% soc 11.5 minutes later battery temp was 60F. Car had sat outdoors for 2.5 hours, then drove about 3 miles on the interstate before the charge. Total charge was $4.45 which works out to about $0.10 per 1% SOC, $0.55 per KWh. Definitely expensive for what you get, but I wouldn’t have been able to make it home without it. Good for emergencies only IMO.

Why don’t they detect that you are charging, and that the battery coolant temp is low, and then preheat it so you can charge more quickly in sub-freezing temps? Seems like a simple SW fix.

Looks like Bolt could use a battery heater that takes power from DCFC. I wonder why they didn’t put one in.

My guess would be inadequate soak time to make a difference. The BMW i3 takes 3 hours to preheat the battery when a departure time is set… I mean it’s like a thousand plus pounds of metal/liquid etc. Imagine the amount of power/time to heat up a medium sized water heater from freezing temps to 70F. At some point the ~ 10% charging losses (a.k.a. internal heat losses) may do a better job heating up the battery than any external heat strips or coolant loop ever could.

The Bolt does have a battery heater. It’s only ~3 kW though.

I am sure the OEM’s size the battery heater to what the battery can accept with respect to max inlet temperature and temp variances. Heaters are not supper expensive.

They could have enabled it at higher temperatures (say turn it on below 55F) and while charging.
Perhaps not the full 3kW, but I guess they’d rather prefer the battery to remain cold, as driving the car will warm it up, and getting rid of heat will be the problem.

Before any Leaf people say “coldgate”, Leaf under same conditions would do similar. Until the battery gets warmer, LiIon should not be charged at full power.

But if Bolt is driven a while before plugging into DCFC as shown in second video (ie, typical usage model in long trips), it starts at 42 kW and sustains 44/45kW the rest of the way. Contrast that with 33 kW average on a Leaf even if it started with 19C in -9C ambient.

Before anyone starts yet another, unprompted p***ing match…. oh, never mind. Too late.

Seriously, people, is it that hard to remember we’re all on the same side and the fossil fuel camp is the bad guys…?

I am not on Leaf’s side, especially due to their crappy AND free charging that’s turning people off EV.

In fact, I do not favor any EV that’s crappier than comparably priced gasser. Even Bolt is crap at MSRP if not for sale and subsidies.

Leaf needs to have a thermal management system, then it would be a compelling vehicle(starting price $30,000 before incentives). Bolt would also be a very compelling option if it supported 200A CCS and didn’t taper so aggressively…

“Average” charge rate is completely meaningless unless you give start and end SoC

20% to 60%

Oops, I was wrong. 33 kW average was from 52% to 70%. I confused 19 kW average which was 45% to 58%. Yes, 19 kW average at -4C ambient at smack in the middle of capacity.

Not my experience. That Temperature I get full (45kW) charging speed after driving in my 24kWh Leaf

Did you watch the video? Leaf slow charging was not due to being cold, but because of battery being too hot even in -9C, 52C above ambient. If you drove a bit, chances are that the battery got warm enough. This explains why 24 kWh didn’t suffer as much since it wouldn’t be charging too long to raise the temperature.

10% to 80% is probably what a lot of people will be using if they have a 230 mile pack. 23 miles in reserve is a decent amount. 20% is 46 miles and is probably overkill. The Bolt charges slowly and tapers early so it is harder to roadtrip without some longer charge sessions if you need to gain a decent amount of AER. I would bet that GM ups its game eventually and gets the Bolt to at least 75 kW max charge rate and little taper before 80% of full capacity, but they won’t do so until the Bolt is completely marginalized by better BEV’s.

Charge my leaf side by side with a Bolt in -10°C temperature. I was getting 100 amps the Bolt 26 amps. I was done in 20 minutes. The Bolt guy was no where to be seen. It’s the Bolt that gives EVs bad reputation. #coldgate is true.

I love your completely made up, fake story. Lol
The Bolt would charge at at least 32 amps if plugged into a L2 station, so your fake story about it charging at only 26 amps hooked to a DCFC is hilarious.

First video at 4:05, the dash message says: “NSA Surveillance Unit HHH”.
What is it about?

It says “Bluetooth device disconnected” above that.

People sometimes give their Bluetooth and WiFi hotspots funny names, like DeepState MIND or KGB Subspace Link.

It’s the nature of the beast.

I disagree that it is a waste of time. If you are in a hurry, it is still considerably faster than charging at an L2 station. Even 15KW is twice as fast as L2 charging, assuming you have a 7KW charger onboard.

In a hurry, yes, but you’re paying 3X the price. Fortunately, cold battery DCFC is unlikely scenario since people generally charge at home, and must drive to DCFC on long trips, which means the battery is warm by the time the car is plugged in.

Actually fairly common for me when I go to the airport. It’s 160 miles round trip and in the winter I have to charge to get home. It’s a cold soak and then a short 10 mile drive to the dcfc charge station. I get a starting charge just under 20 kw, ramping to mid 20’s as the battery warms up. Takes about an hour to get enough charge to make it home.

I know it’s a function of the battery chemistry and gm being conservative on charge rates. Makes me want a much bigger battery ev. 100kwh in a Bolt sized car would be great.

But mommy, I don’t want a good excuse to hammer it out on the freeway heading toward a DCFC… said nobody ever.

I remember a video from Bjørn where he said it’s best to have some range left in the car overnight then in the morning drive it before you re-charge. The driving was the best way to heat up the battery so it was a decent temperature before you started to charge.

Cold soaked fast charging is a hard problem to solve with current gen of batteries. Doesn’t matter how powerful the heater is the limiting factor is the conduction rate through the battery materials. Can’t have large temperature difference between inside/outside of cells. Hopefully next gen chemistries will have better cold charging performance.

That Boston accent gets me every time.

There’s another thing about a cold battery. If you are at a high level of charge you will have little or no regen until the charge level drops some and the battery warms from driving. At a full charge in sub freezing temperatures my Leaf will have no regen at all at first. This is why I avoid charging to full unless going out of town. I want that regen! I only DCFCd once with my newer Leaf and it seemed to take a pretty good charge rate at temperatures a few deg above freezing. It warmed the battery up to about half way. It neither rose nor fell on the 50min drive back home.

This video really made me appreciate the fact that I didn’t get the Bolt.

That’s why there are many of us patiently waiting, in the wings of the Tesla Model Y waiter camp, anticipating that the hatchback EV from Tesla will have by far the fewest overall EV weather and temperature road trip DC FC compromises.

Hopefully the T MY hatchback is worth the wait!

How do other cars perform at DCFC after cold soak?

Even Teslas will charge super slow when the battery is ice cold.

Yes, but how different is Tesla from Bolt? Is it quicker to warm up (ie, bigger battery heater)? And what of other EV, do they heat up better than Bolt? Inside the EV, how do you rank best kW/lb battery heater?

Chemical kinetics … how does it work?

Leaf is actually worse when battery is cold. This is by design for all EVs because fast charging a cold battery can destroy the cathode very quickly. Some EV warm up the battery on their own (active battery heating plus battery self heating by charging). Most notably Tesla warms the battery at a reasonable rate. It doesn’t hurt the cold battery to discharge at a high rate so take it on the highway and drive fast for about 20 miles, then charge. The highway driving warms the battery and then it charges at a reasonable speed. If you L2 charge at home you only need to fast charge after coming close to driving the range of the car in a day and by then the battery should be warm. In really cold weather Leaf can refuse to charge at even 1kW until the battery warms a bit and at that charge rate it can be a very long time before it warms. Bolt is not so bad but still really slow. BTW- I own a Leaf (leased) and bought a Bolt which I’ve tranferred ownership to my son. Will likely buy a Tesla 3 when or shortly after the Leaf… Read more »

“Half as cheap” implies twice as expensive, right?

At home you can set the departure time in the car and charging will modulate to be finished at that time. This is one way to start the trip with a warm battery.
Enroute on cold days I use «L» mode to «pump up» the battery temp via regen before coming up to a fastcharger. It works.

I wonder why they don’t use the cooling mechanism, to warm up the batteries as well?
Put a 1kW heater core in the coolant liquid, should be enough to get fast charging in 20 minutes!

Bolt has a 3kW heater for the battery. But it will only turn it on if the pack starts falling under its operating temperature. It will not turn it on to maintain an optimal temperature.

There is a third space at Burlington sort-of ;^). Many times I’ve parked in the lane behind the cars taking up the spaces and plugged into the charger that’s at the end of the space. You just have to stay with the car. Once I was lucky enough to grab one of the non-ev spaces within range of the charger. The worst time was where there was a phev in one space, then an e-Golf plugged in, but exhibiting an error light. He may have just plugged in and never initiated the charge to get a free close-in parking spot. Fortunately, the chademo plug was able to charge me while I parked in the lane. I’ve been at Burlington at other times and seen PHEVs in the spots and they don’t even bother plugging in.

I would like to see charging at -18C, this week temperature in many part of Canada.

This seems like a bit of an edge case, for times when an EV owner has spent the night away from home base or something. I usually charge overnight, or if I’m away I fast charge at night so I have at least a partial charge in the morning. I’m not disputing the slow charge when cold, but it’s relatively easy to work around.

Here is a question. I have been charging my Bolt at work which is free (Level 2). I drive home during the week and don’t charge at home. The next morning I charge at work again. The idea is to have my company pay for my fuel to work. Is it harder on the battery pack to do this instead of charging at home too? Theoretically, I’m cycling the batteries more by not charging at home. Overall, is this a good strategy? Battery pack wear vs. savings in electricity costs. By the way, my commute is 34 miles of mixed driving.

Don’t see a difference between Level 2 charging at work for 8-10 hours and Level 2 charging at home for 8-12 hours. Nice you have free and, more importantly, available charging at work.

Wouldn’t it be virtually impossible for the battery in a Bolt that had been running through it’s charge for well over a hundred miles to see those temperatures? So, if you’re on a long trip with your Bolt, the outside temperature is not nearly as relevant as this headline implies?

Even a short trip. How much would the battery warm up in a 25 mile average US commute?

Since these are public chargers, it would seem that the driving to them would warm up the battery and plugging in immediately to get a fast charge would be the norm.

This is a Li-on battery issue, not a Bolt issue particularly.

I’ll be home charging on the street which is going to be environmentally similar to a public charge. I’ll come home with a warmed up battery, put it on charge and it should charge at a full Level 2/40A rate. Since the charging keeps the battery warm, it should work fine.

will the preconditioning warm up the batteries?

Check this out. SparkEV 48kW at -6C degrees, all the way to 80%. Since battery is smaller, it’d warm up with less driving.

Flat charges per unit time should be outlawed. They incentivize the suppression of charge rate…

Interesting for sure. My LEAF also slows down when pack is cold but in a much different way with similar results. I start at full speed of the charger but the knee happens much sooner, as much as 20% sooner. Normally I would start seeing the amperage drop with SOC hitting 63-65% with batt temps in mid to upper 80’sº F.

But with batts colder, I was seeing knee as early as 45% with batt temps in the mid 40’sº and did several tests verifying the colder the pack at the start of the charge, the earlier the knee. What it ended up doing is leaving my pack with temps frequently below 70º F after my 30 min NCTC charge.