It sounds like your batteries aren't connected to the system, you're only getting 12 v from the converter/charger. Clean and check all connections, including grounds from batteries to your converter/charger.
Have you checked that any battery isolation solenoid is on and passing electricity? There also is probably a large 80 amp or more circuit breaker or fuse in the cable from the battery, be sure that's passing power on through it.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI