Battery disconnect is for when you STORE the RV and are not using it and it is not plugged in
When camping leave the batteries on, the batteries work all the systems in the RV including the fridge controls
And the converter charges the batteries
Only use the battery disconnect when Storing the RV with out being plugged in
When camping with or without shore power you must leave the batteries connected for things in the camper to work
Things should work from battery when you unplug from shore power
But they can't work if the batteries are allowed to go down, because you keep disconnecting them so they can't be charged
Have your batteries 'Load' tested at an auto parts store
They may not be any good
