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Discussion Starter · #1 ·
The capacity of our replacement traction battery has declined 6% to 7% during the seven months since it was installed. During this time, we’ve driven more than 6,500 miles, including one 1,500 mile road trip.

Our 2020 Chevy Bolt’s traction battery was replaced under warranty on 6 May 2022 by our local Chevy dealer.

The new traction battery now has a capacity of 58 kWh or 62 kWh depending upon the measure used. Torque Pro is reporting 182 Ah, down from 194.3 Ah logged when I picked up the car.

I’ve written previously on the slight battery degradation found on our Chevy Bolt. See Capacity of 2020 Chevy Bolt with 2022 Replacement Battery after One Month, Battery Degradation 2020 Bolt Relative to 2017 Bolt EV, and 2020 Chevy Bolt EV Battery Capacity Anecdotal Observation.

Tracking Battery Capacity

I record three measures of battery capacity whenever I charge to 100%:

1. OBD PID for Bat Cap Est from Torque Pro,

2. kWh consumed & State-of-Charge, and

3. Bat Cap Raw Ah PID.

I also sometimes record the OBD PID for Bat Cap Est and the Bat Cap Raw Ah PID during partial charges.

I won’t explain what these are here. I’ve explained them in previous posts with the exception of Raw Ah PID. I am now recording the Raw PID for Amp-hours since this is used by GM to measure capacity. As you can tell in the accompanying chart, the Raw Ah PID tracks that of Bat Cap Est PID as you would expect if it is used by the car to calculate kWh.

Rectangle Slope Font Parallel Plot


Variability

As others have noted, measures of battery capacity fluctuate from one charge to the next, though there is a general decline in capacity.

Sometimes capacity increases from one charge to the next. For example, the Bat Cap Raw PID increased from 57.9 to 58.2 kWh during the last three charges.

Similarly, during the same charge sessions, the measure of capacity using kWh consumed and SOC rose from 59.7 kWh to 62.3 kWh.

Likewise, Bat Cap Raw PID rose from 181.0 to 182.0 Ah.

Charging Style

I don’t baby the Bolt. I charge to 100% whenever I need to go out of town. And I’ve driven the SOC down to less than 15% on two occasions.

The Capacity Now

We have somewhere around 60 kWh capacity remaining after seven months use and more than 6,500 miles of travel.
 

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Now compare 6 500 miles and 6 to 7% degradation to 150 000 miles and about 10% degradation.
Something is definitely wrong.
One thing is for sure : I pretty much like the empirical test ... the one of draining the battery from 100% to as close to 0% and get the kWh used. Not the PID of a Torque or EngineLink app.

6 months, 0 degradations.
 

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Any time you taking pid values for degradation, you should charge to full and drive down to single digits SOC. Otherwise you will have numbers all over the place.
 

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Discussion Starter · #4 ·
Now compare 6 500 miles and 6 to 7% degradation to 150 000 miles and about 10% degradation.
Something is definitely wrong.
One thing is for sure : I pretty much like the empirical test ... the one of draining the battery from 100% to as close to 0% and get the kWh used. Not the PID of a Torque or EngineLink app.

6 months, 0 degradations.
Yeah, I am favoring the empirical test too as it represents actual driving range.

I think the rate of degradation will decrease as we put more miles on it. I am not worried about it.
 

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In April of this year my original battery on my 2017 was reporting 49.73 kWh.

Then in the last three months I've been traveling extensively putting over 11,000 miles on my car with over 80 DCFC sessions. Running the battery down repeatedly below 10%. I saw that same battery reporting 53.06 kWh at the end of my last trip home last week. It's like the car has to learn how much capacity is really there. And slowly degrades if it doesn't have enough data to go on.

Edit: Just checked capacity today and it's reading 53.63kWh.
 

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...It's like the car has to learn how much capacity is really there. And slowly degrades if it doesn't have enough data to go on...
Yup:
 

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Now compare 6 500 miles and 6 to 7% degradation to 150 000 miles and about 10% degradation.
Something is definitely wrong.
One thing is for sure : I pretty much like the empirical test ... the one of draining the battery from 100% to as close to 0% and get the kWh used. Not the PID of a Torque or EngineLink app.

6 months, 0 degradations.
I wonder if there are several things going on here: first off, lithium batteries degrade quickly when they are first put into service and then they decline very slowly after that for a long time. And second, it may be cooler where this car is, and naturally it will show less capacity in the cooler months. Testing past 1 year to get the warmer season again may show less degradation.
 

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I wonder if there are several things going on here: first off, lithium batteries degrade quickly when they are first put into service and then they decline very slowly after that for a long time. And second, it may be cooler where this car is, and naturally it will show less capacity in the cooler months. Testing past 1 year to get the warmer season again may show less degradation.
Testing and then presenting information based on numbers read of a battery that never went below 10% from 100% is not good. There is a reason why the manufacturers aren't able to give you a solid number of the real capacity of a battery.
 

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My experience has been the opposite, but that is because the tech did not initiate the relearn process when they swapped the battery. I have only measured mine using the kwh used versus SoC approach, I do not have Torque Pro. My old battery was providing about 52kwh after 103K miles. Initially after getting the new one, I was getting about 54kwh and my mile per kwh was showing over 5mile/kwh, which is totally unrealistic for the way I drive.

I did a few charges to 100% with fairly deep discharges to 15-20% but it only slowly crept up to about 58-60kwh. I have simply been charging to HTR and ignoring the data, but my mile/kwh finally came down to about 4.4. Two things have happened recently, I got a new set of tires and the weather in Phoenix has cooled off, but not really cold of course. I did a couple of charges to 100% recently and now the reading is giving me closer to 63-64kwh and 4mile/kwh, which is more what I am used to. I now have 14k miles on the new battery. It just seems like in the last 2K miles with cooler temps and new tires, it suddenly got better.
 
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