My Rushmore comes with a residential refrigerator and 700 watt dedicated inverter, but we went with the RV refrigerator option so we could dry camp without having to run the generator all the time.
Since the dealer removed the residential frig, but left the inverter installed, I sometimes use the inverter instead of propane when on the road. After about 5 to 6 hours on the road, my two 6-volt batteries will be down 30% to 40% when we get to the campground.
Just another instance of the truck's alternator not being able to keep up with the battery draw.