Low voltage circuits have constant draws attached to them. Simple circuits like keeping clocks ticking, and more complex circuits that listen for wireless keys

Low voltage circuits have constant draws attached to them. Simple circuits like keeping clocks ticking, and more complex circuits that listen for wireless keys or alarm sensors. Ideally, they can last for months with those draws, but when the battery is old and cold, it can die in weeks or even days. FWIW, the high voltage circuits (the one with the Li batteries) are physically disconnected with a contactor (a high voltage relay) once the car is turned off. You can literally hear the clicks inside the car as you turn it on and off. All that said, I have heard of some cars which can charge the low voltage battery using the high voltage circuit, but I know nothing of those those are connected.