Are the lights 12v lights or 120v AC lights? If the lights are 12v and they work with the battery disconnected but plugged in to shore power, you have an converter that converts 120v AC to 12v DC. You will need to find the converter and see if it also has a battery charge function. (It may be labeled, but write down make, model and google it.)
You'll need to use long 'jumper' wires, a 12v circuit tester (like this one: Extra Long Circuit Tester
) and a multimeter to trace the wiring from the fuse panel to the mystery wires in the battery compartment. The wires could be to connect to tow vehicle connector, electric brakes, or multiple circuits in RV. It's going to take some trouble shooting to track them all down.