Change the batteries first to see if the problem goes away. There may not be anything wrong with the converter/charger. However, it is a good idea to upgrade to newer technology, the Intellipower 9260 is an excellent choice for your two battery system. Since you need to add water frequently to the batteries indicates they are not coming up to full charge and the charger is always in charge mode.
Chuck & Teri, 1999 35 ft. Dolphin 5350, F53 Chassis with tag axle, Chassis build date 1/99 in Mexico, Banks System, Trans Command, Air Lift Air Bags on rear, Koni Shocks, Blue OX TruCenter, TigerTrak track bars front and rear, Roadmaster 1-3/4" rear auxiliary sway bar, 2013 VW Passat TDI SEL Premium, 1994 36 ft. Avion 5th Wheel. FMCA #F430129