Your right, it’s not and for the reasons you say, and I’m nearly certain that the whole time we drive our cars the 12V battery is being charged at around 14V which is entirely normal and correct for a lead acid battery, but bad for Lithium.
Easy to find out, just check the voltage of the 12V outlet. When the car is ”on”
A good Lifepo4 charger should monitor the battery and when at rest voltage drops below say about 12.7 Begin charging and terminate at whatever “full” is set for.
A lithium bank shoud be disconnected when fully charged, this is tough to do on a car as many alternators can’t handle the battery being disconnected, and of course auto batteries are made for ICE vehicles as they are the majority of auto’s.
Lifepo4 batteries work on ICE vehicles though and apparently tolerate being abused by being overcharged pretty well, I’ve used them on motorcycles where weight is an issue, and on race bikes with total loss ignition systems as the voltage drop is minimal.
I thought having a 12V battery was silly on my Prius and I understand it even less for a Tesla, but it’s the design so it’s what we have.
