a 12V timer would be Good idea. Set it long enough to something but not enough to drain the battery


make sure it the right type. Some are just a delay before they come on. Not a delay before they go off.


some need to be bolted to chassis ground. Pain in the butt to fit


No doubt some will sense the battery voltage and cut the supply if its below a set value.


I have never fitted one as I have no need for one. So can't remand a particular one. But they have been around for decade in the solar power, RV, caravan and boat websites

DaveMcT said:

The snag with that idea is when you forget the switch, the USB will drain your car's battery.

A better option would be to fit a USB voltmeter, then wire in a new fused power socket direct to the battery. You can continue the wire into the boot for cooler boxes etc.

You still risk a drained battery but how often do you have cooler box in use?

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Can add a battery protector that monitors the battery and shuts off before it's gets too low for a start