If you have 12v power when plugged in, lights etc.. work
Then the converter is putting out power, might be low voltage, but it is power
It sounds like there is a break in the circuit between the batteries and the converter/house wiring
This could be a blown fuse, but is more likely a loose disconnected or missing wire
Start at the house batteries
Follow the wire, it should run to the battery disconnect relay
Check voltage on both side ( the big stud terminals )
If the battery side is 11.8v
And the other side is 13-14v you have found the problem
Temporary fix is remove the nuts on the studs and move the battery wire to the charge side, where the good voltage is at, and then put a nut on there and tighten it down
You can do it the other way it needed
Which ever wire is easier to move
Just so you get both wires together
Give it 24 hours of charging, before you unplug shore power, or generator, to give the batteries a chance to recover
