First. unless the coach is brand new the batteries may be at "end of life" one of the End of life indications is lack of capacity. A battery store can test.
IF the store can not test six colt Golf Car batteries on their tester wire two in series and test as a 4D 12 volt.. Same specs.
Second: Light switches often have a small lamp or LED to light them so you can find 'em in the dark, not that I've ever needed that even in a room I've never been before (I carry a flashlight :) ). But they will always have power if
A: the batteries are "CONNECTED" (more on that in a paragraph) or B: you are PLUGGED INTO SHORE POWER.. Either way they have power.
Battery disconnect.. Sometimes this is a switch marked AUX on the dash, sometimes on a control panel inside the RV but by and far the most common place is the entrance.. Positioned so you can reach it STANDING on the ground outside the RV. .May say "Battery" May say "USE/STORE" may say AUX Turn it off (Store is off)