You should check all the batteries at the battery termale . As stated the battery switch should be on. You should have 12.6v or there abouts. NOT 12 volts on each battery installed. If you have 12.6v at all batteries and no power is applied then the batteries are good. If not then plug in to shore power and check voltage on all batteries. Should be 13.x . That will tell you the batteries that have that voltage are being charged. Not all batteries get charge on every RV. Some do and some don't. I am assuming that you only have 2/3 batteries at max, so you would not have a inverter installed. If only one battery nothing would run but a few minutes. If two batteries for the RV side then maybe a TV or something else for a short time.
When you have all AC power off does your refrigerator work? If not when you plug in AC does the refrigerator work then.
