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2018 Bolt EV Premier
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Discussion Starter · #1 ·
My 2018 Bolt EV suffered a front-end collision and most of the front area, as well as the airbag system, were replaced to a hefty sum of nearly US$18,000. My insurance was able to fully cover for this, so I only paid a deductible of slightly less than US$400. It was all fixed up in just 18 days at a direct subsidiary of GM Korea, which seems to be a bit of a minor miracle considering that there are parts shortage going around. But the surprise did not end there and that's what I'm going to talk about.

Some of you may be familiar with getting the battery capacity data out of the OBD-II port. I have a dedicated monitor that displays this data on the dashboard, so I knew that the usable capacity was at 52.62kWh (164.6Ah) just before the crash. The battery has not received a replacement yet, and when I got the car four years ago the initial capacity was 58.63kWh (183.4Ah), so it's been degraded by roughly 10%, which isn't too surprising given the car's age and mileage (~65k miles).

When I got the car back from the service center, the monitor displayed a capacity of 61.89kWh (193.6Ah). I thought that was strange, since that's nearly 10kWh higher than what I expected. But I thought it was just the side effect of repair and possible BMS reset, although IIRC the system would err on the lower side to relearn quickly.


To see how things would go, I drove the car around for around 500 miles, hoping that the capacity would return to what I think was normal. However, it barely budged - now showing 61.60kWh (192.7Ah).

Now, the car's battery pack still has the old VISTA 2.0 sticker on it, and the software still limits the charge to 80%. So at least from the software and external hardware side, the battery's still supposedly the same.

The long distance drive data came out like this.

#1: 78.04% → 12.16% (65.88% delta), 41.9kWh consumed = 63.6kWh
#2: 74.12% → 12.16% (61.96% delta), 37.0kWh consumed = 59.7kWh

So empirically speaking, the capacity does apparently lie around 61.60kWh.

Another thing to consider is that, when the capacity was showing 52.62kWh back then, I did this trip:

80.00% → 2.75% (77.25% delta), 40.8kWh consumed = 52.8kWh

So I knew for sure, with the 80% charging limit I would drain the battery completely after about 42kWh spent (52.62 * 0.8 = 42.096). Therefore the trip #1 after the crash would not have that much battery left in the first place.


I searched around this forum to see what the usual Ah values are for the new battery packs, and apparently it's in the range of roughly 190 - 200Ah.

Since I'm getting numbers in the 193-194Ah range, this falls neatly in line.


One problem is that there is no service record of traction battery replacement for my vehicle. And as I mentioned up there, the car still has the 80% limit set. As far as GM Korea is concerned, that car still has the old battery, and new replacement battery is still pending, subject to availability in the 2nd half of 2022.

So what do you think about this situation? Did the crash magically give me a new battery pack? Is the system still wonky? Would it be possible to just ask for the service personnel to "remove" the 80% limit?
 

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2020 Chevrolet Bolt
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Do you know if they replaced any individual battery modules? Depending on the cause of the degradation, even replacing an individual module might change the capacity.

Normally, I'd just attribute it to a reset of the BMS and say wait a few deep discharges / "full" recharges. But your drive test is hard to explain, unless your SOC would have suddenly dropped from 12% to near 0% and you just happened to stop driving before that happened.
 

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Discussion Starter · #3 ·
Do you know if they replaced any individual battery modules?
If I make another visit to the service center, I'll check on this. However, I have doubts about having partial module replacement bringing the capacity to the whole replacement levels.

But your drive test is hard to explain, unless your SOC would have suddenly dropped from 12% to near 0% and you just happened to stop driving before that happened.
As a matter of fact I was actually expecting this to happen. So I left the car for at least 12 hours so it could reassess the voltage and capacity and whatnot. The numbers did shift slightly, but the numbers I quoted above are for the ones after the stabilization.

I'm going to drive a few hundred more miles to get more data. One more thing I'm tempted to try is to spend something like 45kWh in one shot. That would definitely go over the pre-crash capacity.
 

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2020 Chevrolet Bolt
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If I make another visit to the service center, I'll check on this. However, I have doubts about having partial module replacement bringing the capacity to the whole replacement levels.


As a matter of fact I was actually expecting this to happen. So I left the car for at least 12 hours so it could reassess the voltage and capacity and whatnot. The numbers did shift slightly, but the numbers I quoted above are for the ones after the stabilization.

I'm going to drive a few hundred more miles to get more data. One more thing I'm tempted to try is to spend something like 45kWh in one shot. That would definitely go over the pre-crash capacity.
If you have an ODB2 reader and app, maybe check on the battery pack temperatures? Significantly warmer temperatures will show an increase in capacity, and maybe there's an issue with your battery's cooling system? Again, just guesses since it's hard to explain what you're observing.
 

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12/16 build, 2017, white LT
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My 2018 Bolt EV suffered a front-end collision

usable capacity was at 52.62kWh (164.6Ah) just before the crash.

When I got the car back from the service center, the monitor displayed a capacity of 61.89kWh (193.6Ah).

So empirically speaking, the capacity does apparently lie around 61.60kWh.
I am totally mystified. Keep us posted.
 

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2021 Bolt LT, 2021 Kona EV SEL
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So you're saying if I want my battery replaced, go have an "accident" and I jump ahead of the line? That's what I'm seeing you signal here 😁
 

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The only thing I can think of is that the car isn't relearning the real capacity because it's only being charged to 80%.
 

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Discussion Starter · #9 ·
If you have an ODB2 reader and app, maybe check on the battery pack temperatures? Significantly warmer temperatures will show an increase in capacity, and maybe there's an issue with your battery's cooling system? Again, just guesses since it's hard to explain what you're observing.
Good thing you mentioned that. Battery pack's average temperature is more or less in the same range for both before and after the accident - 25 to 30C (77 to 86F). So I don't see any abnormalities with the cooling system and it appears that the temperature is not a likely factor. Even if it did, all I've seen with large temperature difference was shifts of 1 to 2 kWh at most, not something like 9.
 

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2018 Bolt Premier
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Good thing you mentioned that. Battery pack's average temperature is more or less in the same range for both before and after the accident - 25 to 30C (77 to 86F). So I don't see any abnormalities with the cooling system and it appears that the temperature is not a likely factor. Even if it did, all I've seen with large temperature difference was shifts of 1 to 2 kWh at most, not something like 9.
This is unusual, thanks for sharing @wesley I will be following this thread.
 

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Discussion Starter · #11 ·
Speedometer Car Motor vehicle Vehicle Steering part

I managed to drain the battery down to 0.392%.

White Motor vehicle Vehicle Automotive design Steering part

At that point the drivable range is just 0km. I actually drove the car for 3km with the car showing this in order to get to a nearby charging station. Yes, it was not good for my heart.

So the battery went from 79.61% to 0.39%, so I used 79.22% of it. As shown on the first photo, power consumption was 45.1kWh. That translates to 56.9kWh. This is less than the supposed 61.3kWh calculated from the OBD-II output, but still far more than what I was able to get just before the accident.

Car Motor vehicle Plant Vehicle Steering part

Car Speedometer Vehicle Plant Motor vehicle

This was back in March, with the same 80% charge limit applied. Note how I drove down to 2.75%, but consumed only 41.3kWh. That translates to 53.7kWh.

At this point, I can say that there’s a definite capacity increase outside of the battery’s normal fluctuation. I was never able to spend over 45kWh on a single charge to 80% max since the car’s first year.

Four years ago I spent 44.9kWh energy on the car and the SoC went from 100% to 22% (78% delta).

A year after, it was 44.7kWh with 100% → 19.22% (80.78% delta).

A year more, I got 42.8kWh with 100% → 19.61% (80.39% delta).

So even by that metric the battery was “rejuvenated”. It’s doing better than three years ago. Unless the car crash somehow made the cells “wake up” untapped capacity, it may be more plausible to say that at least some cells were replaced.

Now, I spoke with the GM Korea customer center and set up an appointment to do the real battery replacement recall two weeks later. I’m wondering if I should pay a visit to the service center before that to have the technician check if my current cells are actually new, or just do the swap and re-do the range test to see if it performs the same or not.
 
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