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MYP - Parked at airport 5 days


Supporting Member
Supporting Member
Mar 8, 2021
Mountain View, CA, USA
What makes the 12V battery go dead if you still have plenty of SOC in the main battery pack?

FYI my car stored in CA now (will return in another week, curious to see if my 12V wil be dead; have battery charger):

Screen Shot 2021-07-26 at 5.40.43 PM.png


Active Member
Oct 2, 2020
The 12V battery can fail, i.e. have at least 1 bad cell out of the 6 cells that make up a 12V battery. Assuming a fully charged 12V battery measures 12.6V (they actually vary a bit depending on the type of 12V battery) and you have a dead cell that is 12.6V less 2.1V = 10.5V. Anytime the voltage of a 12V battery measures under 11.5V it is pretty much dead.

12V batteries fail due to physical damage, age, load, temperature and excessive vibration. Tesla vehicles seem to use up 12V batteries every 2 years. The biggest factor in most cases is the electrical load applied to the battery. Of course Arizona summer heat is famous for shortening the life of 12V starter batteries in ICE vehicles too.
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Reactions: srlawren


Sep 7, 2020
Just returned from 10 days parked in the PHX long term garage. Charge was down only 3 miles. This is with sentry mode turned off.

I did have an experience earlier this year with sentry mode on and it dropped about 20% in 3 days. So it appears there should be no concerns as long as you turn sentry off even in the heat.
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