I have spent several winter nights in mine with the furnace on. It draws from the batteries through the inverter. If plugged in to a generator or shore power it will then go through the converter and keep the battery charged or draw from the battery if you needed more current for 12v thus hopefully avoiding the dreaded surge. I have in 10 yrs replaced 1 converter so I'd say if yours gets to 10 years just replace it. Refers are 12, 120 or gas on most RVs.A/Cs require 120v due to amperage requirements. Dougrainer has a good answer.
