It sounds like you have regular wet cell batteries (batteries with liquid acid in them) in your RV.
The voltage level coming from the stock Parallax 73XX converter in your RV once it has fully charged your batteries - if you then continue to leave your converter connected to the batteries - is too high of a level to be kept on regular wet cell batteries continuously. However, the voltage level coming from your converter will bring them up to full charge whenever they are low - but just take longer than other types of equipment designed to put out a higher voltage level for faster charging. Many RV owners replace the stock converters that come in their RVs so that the resulting voltages from their new chargers are better suited to their wet cell batteries for both long term storage and faster charging.
All the above being said, there are different models of dry cell RV batteries available that do much better with stock RV converters. We have those kind in our RV and they are many years old with still most of their capacity left. Our RV sits in the back yard when we're not using it and with our model of dry batteries, the converter can be connected to them almost continuously without damaging them. Hence our batteries are always in full charge whenever we start out on a trip. Our batteries also charge faster than regular batteries, so the converter brings them up to around 90 % of full with only a few hours on our small quiet generator when charging in a campsite. When traveling between campsites, the main engine alternator (our RV is a motorhome) will bring our batteries up to full charge in 4-5 hours of travel time.
RV converters are not always worthless, even for camping without hookups ... as they do play well with certain types of batteries.
