? electrical problem...what’s happening? Should I worry?

Ok the lights going DIM then brightening back up suggests something is drawing one HECK of a lot of 12 volts.
One possibility is bad batteries (They suck the converter down) as suggested up in fact I'd rate 'em high on the list and there are often self-resetting thermal breakers in the main battery line. along with other types that you need to manually reset depending on the RV.

It is also possible something else is sucking 'em down.