Mark- thanks for that explanation. I was wondering about the voltage early on, but couldn't get myself to believe the amps required for that small heater.
When I tested the heater in the TC, if the TC was "plugged in" it would be a trickle charger to the aux battery (and honestly I can't remember if we were charging the battery or not).
So if the issue that you described is the culprit, I suspect there is no way to use that 250 Watt heater in the TC. ????
PS just talked to my hubby. The Renogy is reading 22V late in the day. So that's it. I tested the heater when the sun was up and the solar panels were charging the battery. The voltage was high, higher than it would be at night.
Am I understanding that correctly?