obviously a good way to help with battery run down on a fridge or cooler is to have a lot of cold mass in there. I always add cold water bottles to fill the fridge up. They get colder when the fridge is going off a running engine, at no cost to the battery. Even better, if needed I start with superfrozen ice bottles (0F). Those usually stay frozen several days and will help for sure. Will also help in case I get stranded in the desert and get thirsty. In fact I always have a couple of these in my home freezer as well, for the same reasons and to have on hand for trips. Best to use HD plastic bottles for that. I use large opaque apple juice bottles usually.