[Daryles]

I installed 4 lithium batteries in that compartment alongside the original FLA battery (backup). I didn't want to get rid of the FLA since it was new).
Before installing the batteries I installed 2 layers of 1" styrofoam board on the floor and walls to help keep the batteries warm.
I also put tank warmers on the batteries wrapped them in insulation and put them each in their own battery box.
Lithium batteries do NOT like to be charged below freezing temperatures. You can use them below freezing just don't charge them until you warm them up first.