Airstreams don't come with inverters, which convert 12VDC from the batteries to 120VAC to run household appliances from the batteries. This drains the batteries, sometimes pretty rapidly since an inverter takes about 12 times the current from the batteries as that required to run them on 120VAC.
They come with converters, which convert 120VAC from campground power to 12VDC to run your radio, LP detector, lights, water pump, vent fans, furnace fan, and circuit boards in the refrigerator, the water heater, and the furnace control. The converter also charges the batteries. When not plugged into campground power, the converter is off and all these things run off the batteries, draining them.
I have no idea where the converter is in that trailer, but it's under the couch behind the long drawer in our Classic.