What gauge are you looking at? The little Full - 2/3 - 1/3 red light gauge? If so, that thing is useless. It's looking only at voltage. The voltage is high anytime the converter/charger is operating. An actual battery gauge that uses a shunt like those made by Tri-metric, Magnum, and others will give you 0 - 100% reading of what's in the batteries.
Some RV converter/chargers are notoriously bad. Most people don't really do much camping off the grid thus they don't need a good charger thus the RV builders don't install a good one to save cost.
Don't use the 12v output from your generator. It is also useless. Plug the RV into the generator just like plugging into an outlet and let the build in converter/charger do it's job no matter how poor it may be.