For now vehicles maintenance is focused on electrical system.

It means the following:
* Your car lights can be turned on if your battery is not empty (yes, obviously, but it was not the case in vanilla game)
* Engine can start if your battery charge level is at least 30%. If battery is not powerful enough to start the engine, at least you can still use the battery in some base radio or for spot light until you will recharge it. Below that level, even unsuccessful attempts to start engine will still drain battery even more.
* While engine is running it will recharge the battery depending on your RPM. At idle RPM, alternator will only maintain your lights on without any surplus power to charge the battery.
* A damaged and repaired battery will have a considerable reduced max capacity, but at least you may still use it until you find a pristine one.
* Batteries that you find in the world will never be fully charged, just to be aware of.
* Battery charger will fully charge your battery a lot quicker than car alternator.