Accessory battery was changed last Friday. The next day car is dead

[MikesgreyP85+]

If they just changed the accessory battery 2 days ago and the car is now dead, what else can it be other than a bad battery or a bad installatio?

 

[SageBrush]

they

Who is 'they' ?

In answer to your question, imagine that the 12v had not been replaced and the car died. Any of the possible causes are still possible in your case.

 

[animorph]

DC to DC converter, or whatever charges the 12V battery these days is one thing that can go wrong.

 

[MikesgreyP85+]

Who is 'they' ?

In answer to your question, imagine that the 12v had not been replaced and the car died. Any of the possible causes are still possible in your case.

Tesla mobile service replaced it

 

[vcor]

How old is the car? Possibly the battery ground wire was on its last legs and fell off during the replacement or shortly after. This can happen on old cars, especially if you drive on salted roads (true of all cars).

DC to DC inverter may have already been bad and was the reason the 12v battery died (i.e. no longer being charged). I'm sure there are other possibilities too. Hope you'll return to tell us what failed.