These devices work like a portable refrigerator, drawing power from AC or DC power (like the 12-volt plug in your car) to keep your food cool and dry. Ice is nice—until you do the math. For an ice chest to efficiently keep your perishables cool, you need twice the volume of ice as the volume of food and drink. That means, for most coolers, only a third of the available space can be used for supplies; the rest needs to be devoted to ice. Enter the electric cooler, which functions like a portable refrigerator or freezer that plugs into your car, a generator, or a large portable battery. These devices don’t need ice, so nearly the entire interior space can be used for your comestibles. I say “nearly” because you need to leave gaps between items so air can flow amongst the brisket and brewskis. Usually, the different shapes of the items naturally create enough space between themselves to let the cold air circulate. Both designs share the same off-grid problem: the coolant, whether ice or electricity, will run out at some point, ideally not before you’ve consumed all the food and drink or before the trip ends. My family and I recently tested a few ice coolers alongside some electric ...