Are you sure about that? There could be some logic where the BMS only actively heats the battery for 24 hours or something before giving up and conserving energy, which could explain why you see temps reach ambient eventually when you leave it for a week.
I have used Scan My tesla since the car was new, also use teslalogger so all scan my tesla data is logged and I also have teslafi logs since new. (2 1/3 year).
The teslalogger logs also shows when battery heating is active, and it just aint when the car is parked.
I think this section of the manual is what led me to believe the car may use battery to keep the battery warm while parked:
View attachment 929127
Is that picturere from the most recent manual or from the online version?
I can not find that i formation.
I live in a cold climate.
If I leave the car at work not driven for a week (outside) the battery temp goes down to the ambient. It takes a while to reach ambient but during this time no energy is drawn from the battery.
I can see when charging outside in cold with the UMC charger at low power (2-3kW) that the battery heat needed to keep the battery at least a little above freezing is way more than sentry mode. Like closer to 1 kW or so, so the car would drain from 100 to 0% in a few days, if this was true.
If plugged in as recommended we really only have two choices, either use scheduled charging or not.
At scheduled charging the car will be charged each day, which heats the battery either by charging alone, or if the cell temp is below freezing also by heating the battery.
If not using scheduled charging, I havent really ised this much, but then the charging starts as soon as the cable is connected, and I guess re-charges quite often if needed.
Why would the car use energy to keep the battery warm? It would be expensive in terms of electrical use, and also increase the cycles on the battery.
The car was connected (UMC) and chsrged in the morning of 25DEC 2022. This means, the battery was kept at at least 8-9C during charging.
This is the same day, 5PM
ambient = -19C for borh pictures.
This is the same day, 10PM
I also might have logs, but the logs is only active when the car is not sleeping (sleeping - HV batt disconnected so no battery heating) and the tablet mostly shut down due to too cold when parked.