[Tiara Open] 2006 36' Cummins QSB. Batteries test good with load tester,but dont hold charge

[Sans Peur]

I have had wiring that looked good create a good amount of resistance. Test the batteries at the terminals then at the main switches. The wires are in a very moist environment and can wick that moisture up a good ways. As current is drawn through it will start heating up and cause a voltage drop from the resistance. As JClarke003 said Meter Everything in the stream.