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Old / Failing 12 V Battery may interfere with Car Going into Sleep Mode

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Duma

Member
Nov 16, 2014
169
72
Since I haven't been able to find any posts on this topic, I bring this hypothesis to the community.

I've been on TeslaFi monitoring service since August 2016. Among the items monitored is when the car goes into sleep mode. During that time, I never had a problem with my Model S failing to sleep (except when I changed to settings known to interfere with sleep). Beginning in August 2019 my car no longer was willing to sleep. Settings were fine, logs show TeslaFi giving the car a chance to sleep. Nothing helped and I was busy with other matters. The increase in vampire drain overnight was noticeable but not enough to be an issue.

Fast forward to November, 2019 and my car gives the alert to have the 12 V battery service/replaced. Tesla replaced the battery yesterday and with no other actions on my part, the car is back to sleeping just fine. There wasn't even a software update to the car, so the only change was replacing the 12 V battery. (Aside to the other old timers - this is my first 12 V battery replacement, so I got about 4 1/2 years. Not bad given about all the concerns back in 2015 and earlier with many 12 V batteries failing after a year.)

Most of the time, the additional vampire drain from failing to sleep is not a big deal. However, if the car will be left parked for a week or more without being plugged in, the additional loss in charge could be an unwelcome surprise.

The increase in vampire drain due to the car failing to go into sleep mode may be an early symptom of a 12 V battery reaching end of life.

Caveat. My car has AP1 and the MCU1 control unit, so it remains to be determined whether cars with the newer control units behave the same way. In any case, it will be a few more years before the 12 V batteries degrade on those cars. For now, I expect this to be an issue mostly for older Model S.