Battery doesn't work unless connected to house or TV
I have a Fun Finder X-139, the smallest model. I have one battery I keep on a trickle cell charger all the time except when I'm camping
If the battery is hooked up to the trailer, and either:
RV hooked up to house or campsite current
Trailer electrical hooked to TV for towing, like for lights, turn signal, etc...
The RV interior lights work. But if the battery is connected without an external hookup, either house current or TV, then the interior lights do NOT work.
The battery is fine. It was checked at Batteries Plus. It is fully charged and holds a charge fine.
It is hooked up to the trailer fine. Positive to positive, etc...
This will be an issue if we ever go dry camping.
What kind of things should I look for to solve this problem?