Borski has useful info above. Road trips can be fun having a fridge / freezer for bringing food along or buying from farmer's markets or rare food places. Useful along the way or for bringing things home at the end. Bringing things for a meet up with friends. The ice cream example is a fun one, or another cold treat on a hot day and drive. Or for bringing some cold snacks from home, or even some meals for the microwave at the hotel in case we get in late and want to save some time.
The Dometic also plugs into AC, so can be plugged into a hotel's wall power if we want to free up the trunk, at our destination. No built-in battery on this Dometic model, but the outlets on the Gravity are nice with it. After reading some reviews, and how we would use it, we opted for this one.
It seems to be very stable with temperature and a big jump up from the ice coolers we used before that tend to make a few kinds of food spongy with the temperature variation, which this one has not had for us. Much like products from a quality
beverage cooler manufacturer, it maintains consistent cooling performance. I think both options above have their benefits.