Still don’t understand voltage…

[icrude]

So I recently bought my TM that came with 2 6 volt 225ah batteries. Who knows how old they are. I had them plugged in for at least a day. I would assume they charged up. We go dry camping and don’t use any power other than a light here and there. The fridge is on propane. The furnace does kick on every now and then at night. When I wake up the voltage is at 11.6. Now my basic question is, should 225ah batteries deplete that much over one night just because of the furnace, lp fridge, and a few lights? I know there is small draws here and there also, but 225ah batteries are pretty big, I could think maybe 75% charged in the morning, but down to 20%? That makes me think the batteries are bad.