Using a battery to produce heat is typically a big drain...
We cold weather camp a few times a year and with flannel sheets (an absolute MUST) and a down comforter or down sleeping bag opened up like a comforter, we are ok down into the low 50s.
It's rough getting out of bed but it's all part of the adventure. I typically jump up and turn on the LP furnace and get dressed while standing over the floor vent.
Then I put the stove top coffee percolator on a burner and light the oven to pre-heat for biscuits or sweet rolls.
The trailer heats up quickly and I don't use that much battery in the process.
Then it's a hearty breakfast and a hike in the woods if we're lucky and the weather cooperates.