In the UK you have mostly 24 v systems so you are far more likely to have it support a cool box for at least 12 hours. In the USA we have 12 v systems, I have this fridge.
I leave it plugged in for 10 hours overnight and eve though I thought it would drain the battery it doesn’t, it has a fan which is running constantly but has no such effect. A lot of trucks here have built in fridges which are even bigger and reading the manuals they advise not to switch them off unless the truck is not in use for more than 48 hours.