Battery was doing fine on the fan but the lights deadly

Fastfwd75 wrote:
The battery level indicator tells me nothing and the black water level stopped working after 2 weeks. At least I can still check on fresh and gray water.

That's typical. When you were with the salesman in the lot, it all sounded like it was built like the space shuttle. You'll find that it is built more like a cheap toaster.
I'd suggest you get an inexpensive multimeter before embarking on a long trip. The meter will be one of your best tools to diagnose and fix electrical issues in your RV.