The converter is trying to charge a dead battery and most likely going off on overload. The converter can not supply the current necessary to charge a dead battery.
Disconnect the battery and charge it with a battery charge for 24 hours and then test the battery. It should read above 12.7 volts once disconnected from the charger.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles