Let me start by stating that requiring the battery to open/close doors is a bad design choice overall. There should always be a way to open the door using a physical key.

Ok, having said that, the 12V is a better choice. It’s easier to replace a 12V battery in case it fails and forcing the main battery to power everything runs the risk of draining that. Li-Ion batteries don’t react well to being completely drained.

Besides, all EVs have a way to attach an external battery to the 12V system in case of total power failure, which will then allow you to do whatever you need. In case of Tesla Model Y there are two cables hidden in the tow eye cover that power the hood release. With the hood open you can charge the 12V battery directly.

So, how much time do I have before I have to switch to Servo?