Question for you vets. I have an old Beaver Contessa (1990). I've had it for many years and never a (major) issue. I just installed (2) new battery's and I recently took a 250 mile trip with zero prob...
You should have either a converter or an inverter/charger. Either of these units should charge the batteries. They may or may not charge the chassis batteries. I would guess by year you have a converter. It could be failing and you are running off battery power. Look around the 120 volt AC circuit breakers for a converter. It maybe located outside near where the shore power connects to the rig.