Hi everyone,
I recently bought a 2023 Chevy Bolt EV from a local company that imports these cars to Ukraine.
The car had already driven about 29,800 km / 18,516 miles before I bought it. I am currently quite stressed because I cannot figure out how to correctly calculate the battery capacity and state of health.
I tried to get the battery capacity through an OBDII PID. The formula used by the scanner seems strange to me. It uses a coefficient of 0.0032, but I cannot find a clear explanation for why that exact number should be used. With this formula, the scanner shows around 55 kWh of battery capacity.
Then I tried another method. I used the energy consumed between two battery percentage values and extrapolated it to 100 percent.
The formula I used is:
estimated capacity = used energy / (SOC difference / 100)
For example:
d = (c / (a - b)) * 100
where:
a is the battery percentage after chargingb is the battery percentage before chargingc is the used energy in kWh (got via OBDII and confimed via dashboard)d is the estimated usable battery capacity in kWh
The strange thing is that this calculation gives different results depending on the starting and ending state of charge. The larger the SOC difference, the higher the estimated full capacity becomes. The highest value I got this way was about 60.9 kWh, which is much higher than the 55 kWh shown by the OBDII PID.
I also tried calculating capacity using amp hours and voltage:
Wh = Ah * Voltage
kWh = Wh / 1000
Using that method, I got around 60.95 kWh again.
So now I have several different numbers:
OBDII PID formula: about 55 kWh
Energy used between SOC values: starts at 50 kWh and goes to about 61.9 kWh
Ah multiplied by voltage: about 61.95 kWh
I understand that there may be buffers, nonlinear SOC reporting, temperature effects, voltage variation, and possible differences between nominal, usable, and estimated capacity. But I still cannot understand which value is the most reliable for estimating the real battery health.
Has anyone with a 2020 to 2023 Bolt EV dealt with this before?
What is the correct way to estimate the usable battery capacity and battery state of health on this car?
I would really appreciate any explanation, because I have been stuck on this for a while and it is stressing me out, and my obssesion not allow me to sleep well.