Furnace/Battery Help and Black Water tank

Colder weather coming on! Tested my heater, works well. My question here is how much battery power, if any, does it use to run it or does the propane do it all. I am going out camping without hookups. How best to have some warmth without draining the battery.  I don't quite understand if the thermostat is powered by the battery when no hookups. For that matter, does the water pump have the assist of the battery?And the black water tank. This year the read out inside always reads "3 lights", whereas the grey water goes down to "1 light. when I have dumped. . The grey water  starts (when I start to dump) with 3 lights , goes down as it should. I read that something may be hung up on the level gage and only way is to keep an eye on it, if it is constant in this reading. OR take it to your dealer.  Dealer is some way from me, that would not be bad, but they may have it for months before I get it back..   Comments if anyone has the problem and any suggestions.