How long should a charge last?

Maybe you could take the batteries to the RV dealership, without saying where they came from, and have a load test done. This is usually free with a kind of understanding that you will buy new batteries if needed. In your case, if the batteries are shot you should be able to use the warranty. In my experience most batteries have at least a year of no questions asked replacement.

I have a house disconnect switch that shuts off all loads on the battery. That way I can go two winter months without charging. If your switch isolates the battery or you just disconnect a battery cable you probably will have to disconnect or switch off the solar panels from the controller because the battery controller will likely be very unhappy.

That advice about waiting several hours before trusting the voltage chart for state of charge is important. I lost a set of batteries not following that. If you want instant reading of % of full charge a battery monitor that counts amp hours in and out is necessary.

Thanks to the poster for the amp hour calculation on the propane alarm; nice to know how to calculate the discharge time for the battery.