I've just got an electric cool box with a 12v plug for the car. if I left it on all night would it drain the battery (I have no idea if 12v is a lot or not)?
There will be more out put in the Cool box than your car clock Meg, I would not leave it on overnight for the main reason ( Fire) If the box overheated it MAY set the electrics on fire. Leave it until your journey begins.