Running the fridge on 12 Volts?

I am by no means an expert, but my 2008 trailer has a Dometic fridge that seems to work off 12v. The fridge has an auto and gas setting. If I leave it on auto and unplug I can go around and not hear any signs of gas or hear the click click of the pilot lighting. I don't remember the last time I set it to gas only, but I do remember hearing the "furnace" type sound.

None of the AC outlets in the camper work unless I am plugged into a generator or campground, so I assume I don't have an inverter?