Recently we have accidentally left our 300SE's doors open, i.e. the dome lights on, overnight (we are slowly adapting to our new life with our second boy ;-) ), and obviously had the unpleasant surprise of a dead battery the next day.

Which made me think that it would be very useful to have two things on a car:
* An automatism which would switch off the battery when the minimum reserve needed to start the car has been reached. I.e. an automatism similar to that existing on laptops.
* A voltmeter, which would let you know when you have sufficiently recharged the battery after jump starting and letting your engine run to refill it.

It seems that voltmeters were common on older cars. I wonder why they were apparently removed from newer ones.

I have however never heard of a laptop-like, automatic battery switch off automatism on vehicles, which would however be critical at times...

Any opinions, additional information, etc.?

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1991 W126 300SE (M103)
1995 W124 E320 Wagon (M104)