The converter would prefer to have a battery attached. The load of the battery smooth out the voltage from the converter and keeps it within an acceptable range that. No battery load the converter will put out close to 14 volts. If you have a large draw with all the lights and the heater on you may exceed the capacity of the converter. The battery would provide that additional current.
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