Just to add my pennyworth, we also have a combicool and are really please with it - the only problem is that if it is very full it can get over enthusiastic and freeze things you don't want it to. Only used it in anger on mains, but the gas ran well in test. Don't know about 12 volt, though I wouldn't expect too much.
It is well insulated, and being top opening keeps the cold air in, unlike a front opener.