Is this a plug in that was used before, or is it a brand new plug in location? Usually what happens in a new location is someone does not understand RV plug in wiring, and puts 240 volts onto the receptacle. Then, she blows up and takes out lots of problems.
Lights are dim because the batteries are fully drained. Get a battery charger onto the batteries ASAP.
Have a competent electrician check out the receptacle wiring to ensure it is correct. Check operation of fridge, TV, and other appliances in the rig that can run of 120 volts.