When plugged into "shore power" an older converter charger charges the house battery very slowly unless it is a new "smart" charger like the PD 9245. You must have the auxiliary battery switch "on" to get charge current to the house battery. Check battery electrolyte levels, it should cover the plates.
Check battery voltage with a multimeter on the 20 volt dc range. Should read 13.6 to 14 volts with RV plugged into shore power and charger working. Check cables that run from the converter to the house battery for tight connection. Cables connect to coverter/charger with allen head set screw terminals.
There is a latching relay that connects the auxilary battery switch to the house battery. Listen for snap sound when you turn aux battery switch on or off.
The relay sometimes sticks or becomes defective with continued use.Check connectors at battery terminals for corrosion and tightness, must be kept clean and tight for good charging. If this is beyond you, have an RV service check it out and watch them to learn if possible.
House battery charging system, wiring, maintenance and troubleshooting is good to learn and will always come in handy.