SOC drops 5% in 2-3H after being unplugged

[Nabush]

All,

I've been parking and charging my Model 3 outside for the past 6month. But I noticed the issue before as well...

I usually charge to 65% drive to work, arrive at 60%.
I work 12-13H, come back to the car and battery shows 55%. No sentry mode, no cabin overheat.
Battery temperature more or less the same as when I left in the morning (I have scan my tesla). If I precondition in the morning battery is at 52F. Battery is around 45F at night. Not a big difference which would explain 5%.
This only happens the first time I unplug the car, and looking at it it happens the first hour or 2 after the car is parked. If I leave the car unplugged the following days SOC does not move anymore.
I think this is an issue with the BMS estimating SOC while plugged.
Since I have the car I never charged to 100%. Might be the time to do a full charge to allow cell balancing... (I will look at my cell voltage in scan my tesla today to see if I see difference in voltage per cells).

It looks like it is a pretty common observation right ?

Thanks

 

[Nabush]

All,

I've been parking and charging my Model 3 outside for the past 6month. But I noticed the issue before as well...

I usually charge to 65% drive to work, arrive at 60%.
I work 12-13H, come back to the car and battery shows 55%. No sentry mode, no cabin overheat.
Battery temperature more or less the same as when I left in the morning (I have scan my tesla). If I precondition in the morning battery is at 52F. Battery is around 45F at night. Not a big difference which would explain 5%.
This only happens the first time I unplug the car, and looking at it it happens the first hour or 2 after the car is parked. If I leave the car unplugged the following days SOC does not move anymore.
I think this is an issue with the BMS estimating SOC while plugged.
Since I have the car I never charged to 100%. Might be the time to do a full charge to allow cell balancing... (I will look at my cell voltage in scan my tesla today to see if I see difference in voltage per cells).

It looks like it is a pretty common observation right ?

Thanks

I have 12mV imbalance between my cells. It is not a lot but not sure what is a normal value with Tesla BMS

 

[jjrandorin]

It looks like it is a pretty common observation right ?

Right, lots of people observe this so I would agree its common and nothing to worry about.

 

[KenC]

All,

I've been parking and charging my Model 3 outside for the past 6month. But I noticed the issue before as well...

I usually charge to 65% drive to work, arrive at 60%.
I work 12-13H, come back to the car and battery shows 55%. No sentry mode, no cabin overheat.
Battery temperature more or less the same as when I left in the morning (I have scan my tesla). If I precondition in the morning battery is at 52F. Battery is around 45F at night. Not a big difference which would explain 5%.
This only happens the first time I unplug the car, and looking at it it happens the first hour or 2 after the car is parked. If I leave the car unplugged the following days SOC does not move anymore.
I think this is an issue with the BMS estimating SOC while plugged.
Since I have the car I never charged to 100%. Might be the time to do a full charge to allow cell balancing... (I will look at my cell voltage in scan my tesla today to see if I see difference in voltage per cells).

It looks like it is a pretty common observation right ?

Thanks

Do you mean something like this, but the reverse:

In my case, I live down in a cold spot on a lake, so that in Winter, I'm usually much colder than the areas around me, so as soon as I drive somewhere, the ambient is warmer. The above, I remember, I went to an appt, and the car sat in the sun for a couple hours when I got back, so it was warmer than when I left in the morning. I'm guessing the BMS is calculating based upon the original cold ambient temps where I live, and then when I get back in the car, the ambient was higher, so it recalculates based upon the warmer ambient.

The opposite happens when I go somewhere, where the car sits somewhere colder.

 

[AlanSubie4Life]

I think this is an issue with the BMS estimating SOC while plugged.

Yeah pretty common. In general in cold weather, SOC estimate can go up or down when car goes to sleep. In warm weather, the SOC estimate can also go up or down.

5% is kind of high (especially if it always moves the same way regardless of temp) but seems to be common on some cars.

I don’t think the behavior has much to do with being plugged in (as long as charge threshold is below the SOC).

As @KenC pointed out, could look at the energy screen details to see whether you sometimes see a bump up.

Last time I was in a cold environment my car gained 4 rated miles sitting overnight. After an additional three days, I had lost three of those, for a net gain of one.

 

[Nabush]

Yeah pretty common. In general in cold weather, SOC estimate can go up or down when car goes to sleep. In warm weather, the SOC estimate can also go up or down.

5% is kind of high (especially if it always moves the same way regardless of temp) but seems to be common on some cars.

I don’t think the behavior has much to do with being plugged in (as long as charge threshold is below the SOC).

As @KenC pointed out, could look at the energy screen details to see whether you sometimes see a bump up.

Last time I was in a cold environment my car gained 4 rated miles sitting overnight. After an additional three days, I had lost three of those, for a net gain of one.

In fact I checked :

Drove 68 miles this afternoon. Started at 59%. Arrived at the house at 34.5% (Hilly roads with significant elevation changes, mid to low 20's). Did not plug the car. SOC is a 37% now and it is 15F, so it went up despite being super cold. Battery was at 62F when I parked the car, probably in the 40's now... Weird..

One thing is sure, having MPP suspension parts /Coilovers and a very low car helps for efficiency significantly...