12 volt battery charging

[Patrick W]

I understand that the Model S's 12 volt battery is charged by the main battery pack (correct me if I am wrong).

Is it constantly being charged or (as I read on another site) is it only charged when the main battery is plugged in and being charged?

 

[jerry33]

The 12V battery charged as needed. When plugged in and not charging, the system wakes up and checks every so often. When not plugged in, it still wakes up and charges every so often. This is one of the causes of vampire drain.

 

[Patrick W]

The 12V battery charged as needed. When plugged in and not charging, the system wakes up and checks every so often. When not plugged in, it still wakes up and charges every so often. This is one of the causes of vampire drain.

Just what I needed to know. Makes much more sense than what I read on that other site. Thank you.