12v spare?

[ATPMSD]

I'm not sure it would be drivable if it has a dead battery. If the battery is really dead, I don't think a jumper from another car would revive it.

You are not trying to revive the battery, just supplying power to close the contactor to power the DC-DC transformer to allow the HV battery to power the 12V system. So if the battery is dead (drained), can you can jump the battery to wake up the car. If the 12v battery has failed internally, then you are likely screwed as the BMS may shut-down the car.

 

[beatle]

If you wait until it needs to be replaced it is a warranty item and will be replaced for free.

Tesla charged me to replace the battery on my 2015 under its extended warranty. I asked and they said it was a wear item.

 

[ATPMSD]

Tesla charged me to replace the battery on my 2015 under its extended warranty. I asked and they said it was a wear item.

That makes sense as the battery is not covered under the extended warranty, only the original.