Can cell balancing cause vampire drain?

[pep_dj]

Some nights (I leave it unplugged at night) my M3 is losing between 4% and 8% battery (no sentry, no summon, no apps waking up the car, no overheat protection...)

I asked Tesla, and they answered this:

The consumption that is perceived is a battery balancing, which tries to equalize the charge of the battery cells to provide better performance and more accurate data readings. This is the expected operation.

Do you agree? Is this ok?

(Sorry for my bad English)

 

[GtiMart]

Do you charge at or over 90%? I'm under the impression balancing on model 3/Y only happens at that point.

The other thing to know is that as the battery cools down, less energy can be extracted from it. That is not the car spending energy, it'S just a fact (physics/chemistry) that less energy will be output from that battery unless it warms up again. The car shows that by reducing the %SOC indicated in the car.

 

[pep_dj]

Usually I charge the car at work, until 70%. In the afternoon, I go home (less than 10 miles), and I leave the car unplugged all the night.

Here you can see the info from the car. It's in Spanish, but you can see that the power drain comes from "Vehicle standby" section:

 

[GtiMart]

Yep. The rest shows that you did not leave the car awake (no sentry etc). I believe what you are seeing is just your battery cooling down. I presume that even in Spain, at night temperatures will go under 20C...

 

[pep_dj]

Yes, about 10º at night. So, if I understand correctly, the battery is hot because is charging at work, and then, because the battery is colder at home, the next day, the % of the battery is lower?

 

[GtiMart]

That's at least a part of the reason yes. 8% is a bit high though, some energy is being spent somewhere. Maybe charging the 12V, that happens from time to time and uses a bit of power.

 

[Park2670]

I am curious if it is actually burning 8%, or if it sees the drop and puts it in that category.

Very possible that since the BMS is not seeing much variability in charge, that it stops charging at what it thinks is 70%, and after it sits changes its estimate to 62%. Then it sees that as a "loss" even though its just an estimate change.

 

[GtiMart]

Ah yes, BMS recalibration is also another possibility. SOC is just an estimate, it's not a very precise number, and the BMS sometimes readjusts after the car has slept for a while. Thanks for bringing that up.

 

[pep_dj]

Thank you. Maybe I should try recalibrating BMS and balancing cells by leaving it overnight at less than 20%, and charging it to 100% next day... right?

Anyway, 8% seems a lot to me...

 

[Park2670]

If its an LFP battery, could be pretty normal.

 

[pep_dj]

Mine is not LFP (I see daily and trip in the charging menu)

 

[AlanSubie4Life]

This is an issue several have noticed and I think it is a new one. There are frequently reported large BMS adjustments. I see them too.

I don’t think this is well understood at this point. (Aside from the general understanding that BMS adjustments do happen.)

I don’t think it is due to the new tracking system just making the changes more evident.

Still, have to determine whether negative adjustments (gains) reduce the tabulation of park losses (I don’t know whether they do - I do know that negative losses (gains) do not allow display below zero on the park screen). It may be that these BMS shifts balance out (though I don’t think so) over time.

TBD! Keep phantom drain under control