Consistent drops in SOC every time vehicle is turned off and on.

[A.K.]

Hello,

I'm looking for advice on strange behavior I was able to observe on my Kia Soul EV 2018 (30kWh, 80Ah battery). Every time I turn it off and on again the SOC drops around 2.5%. It looks like it must stay in off state at least for some time for this to happen, but I have not determined minimal duration yet. The drop is more or less the same value irrespective either it was due to quick visit to supermarket, overnight stay at home or whole day parking at office. I checked it with Soul EV Spy and could see corresponding increase of around 0.8kWh in accumulative discharge power. The accumulative operation time also increases. I could see it going up by value starting from time car was off till about 2 hours.
So it all looks like car is having some kind of secret life by itself. I wonder if that is known behavior and part of normal behavior or should I worry?

 

[JejuSoul]

You don't give us enough info to make a guess.

Examples
Do you live in Northern Canada or Alaska? My guess - battery heater.
Do you live in Dubai? My guess - battery fan.

At what SOC was the car when this happened?
Do you live on top of a hill?
Have you looked at the data for the 12V battery? Is it being charged?
Have you looked at the cell voltages of the main battery. is re-balancing occurring.

 

[A.K.]

Thanks a lot for answer. Here comes more context:
I live in Europe. Car came from official dealer, so most probably designed for this reqion (54 deg. latitude). Neither south nor north, moderate climate. So far the effect was noticed at temperatures around 0-10 centigrade. I have no results for other temperature range yet.
Landscape is mostly flat, no significant altitude variations all the places I go during the day.
I do not yet know how to collect information about 12V battery. Any tool for that (Soul EV Spy seems to have a lot of information but it is not always clear what each parameter means)? Anyway 800Wh would literally blow 12V battery apart.
Cell voltages are balanced well. At stationary I never saw the delta bigger than 0.02V and that seems to be just the resolution at which BMS is reporting.
I typically keep battery between 25% and 83%, occasionally letting it to charge for unlimited time to give BMS a chance to re-balance cells.
I do not know how to check if BMS is doing any re-balancing at particular moment. Any suggestion?

 

[JejuSoul]

Okay. there is something strange going on.
The main battery is normally 'disconnected' while the car is off. Only the 12V system stays on.
So my suggestions for recharging the 12V system or re-balancing cells are not normal.
To recharge the 12V system the car needs to be on and have some load eg headlights.
Calibration or re-balancing occurs at the end of a charging session.

For your car something unusual is waking up the car and keeping it awake for two hours.
My guess today is that you have the climate timer set to turn on the car and warm it up.

 

[A.K.]

Thanks for suggestions. Unfortunately it does not look like climate control is involved as there is no preheating schedule active. And it happens irrespective of time of the day. But maybe charging schedule could cause such behavior, I dunno, will try to check.
Currently I have 2 hypotheses:
1. After idle time BMS performs some kind of remaining charge recalibration by cell voltages.
2. BMS reports consumed energy (or part of it) with significant delay so it takes some idle time for those number to settle in BMS and reach display.

I wonder if pulling the safety plug for a night would be safe enough procedure? That would allow to narrow down this behavior to battery or other electronics of the car.

 

[JejuSoul]

Have you read this thread :- Latest E400 BMS update appears to have reduced usable capacity.

Did the glitch you are noticing begin after the 'fire-safety' recall?

 

[A.K.]

I own this car for less than a year and have not been at local dealer for maintenance yet. Online check at https://www.kia.com/eu/service/kia-overview/service-and-maintenance/kia-recalls/ shows no pending recalls for this car. So chances are it has upgraded BMS. Is there any way to check BMS firmware/hardware version?

I read that thread (very interesting) and found no similarities to my case. Maybe I missed something.

Your suggestion that car may be performing scheduled heating gave my an idea to check for possible software glitches related to that feature. Originally both climate scheduling slots were empty. I filled both with arbitrary data and marked both as OFF. I also turned OFF charging scheduling and manually turned heating off before leaving the car. After more than 2 hours SOC stayed the same 32.5% according to Soul EV Spy. Interestingly cumulative discharge power still went up by 0.2kWh. But cumulative charge power ALSO WENT UP - by 0.1kWh. So some BMS tricks are definitely involved here. As overall battery voltage also went up by 1.7V, so maybe BMS applies some corrections and recomputes kWh and Ah values a bit. Guess I will have to collect more statistics at different settings and surprise dealer with few tough questions.