Originally Posted by adonh
...Never connect heater to a power converter without a battery in line. Be sure that the heater is connected to a "filtered" (pure DC) circuit of the converter.
The heater controller is obviously sensitive to "noise" on the DC voltage. Older converters are notorious for poor voltage regulation, which is improved with a battery in the circuit. If you have an older converter, just make sure you always have a battery connected if the converter is powered up.
If you have a new converter, this is less of a problem. You won't find a special "filtered (pure DC)" output on the usual RV converters. I haven't seen one on any converter.
Don't worry about it. There's not much you can do, anyway. Just get the polarity right. BTW, with a modern converter you can probably get away with no battery in the line--they are pretty good--but I wouldn't do it on purpose. If you think about it, there are times when you're plugged in (so the converter is powered up) and you decide to switch out the battery. Oops.