Another trick if you have room is to put "blue ice" packs in freezer when plugged in. Move them to fridge, packed around sensitive items (beer and milk). they will extend the life of your cool as long as you don't open it. Keep in mind, it takes 10 times longer for that fridge to cool down once plugged back in than a residential model. You can also move a few things into coolers during the non-powered leg of the trip.
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