[VeryTallMidget]

If you want to make it even more realistic, add a wear system to battery, then player needs new battery after some time.

It could take to account the overall usage time and the times that battery has been very low.
Lower it gets, quicker it will wear out.

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Server was empty, no one there... Battery system is working and I stopped the engine, kept lights on and it discharged battery like it should, also I drove without licence and violated speed limit two times

Annoying is that everything is done by long commands. Can car ignition be just a key on the keyboard?
I guess if everything is made very simple, more players will play.

In BlackTurbo CandyGirl server everything is quite simple and easy.
I had a plan to make a business server from the same game mode used there, but its too much work.