LIthium battery heater
Lithium batteries do not like to be charged at freezing temperatures.
I have a 5th wheel RV. The battery compartment is the forward compartment under the overhang. It is not heated. First, I added extra insulation. Two layers of 1' styrofoam board.
I used an RV tank heater 7"×24". 12v, 6.25A, 75W. The built in thermostat turns on at 45°F off at 65°F (I would have preferred it turned on at 36⁰F).
The tank heater pad has it's own adhesive. I chose to tape it to the battery at one end (so I can remove/adjust it) and wrap it around the battery. Tape the insulation to the battery. Wrap it around the battery AND the heater, leaving 3" of the heater exposed at the wire lead end. This end has the thermostat. Leaving it OUTSIDE the insulation will ensure it is exposed to cold temperatures. Put the entire assembly in a battery box (to anchor it down). This battery heater is wired to my FLA battery via inline fuse and a switch. I did this because the FLA battery can be recharged at any time above or below freezing. I turn on the switch if below freezing temperature is expected. I have insulated my battery compartment and have a remote thermometer in the compartment AND the battery monitor Victron BMV-712 has a thermometer attached to the battery.
While my 5er is stored for the winter I have added a 120vac outlet in my battery compartment and I use a 120vac 75W plug in battery heater. I have it laying along the floor of the front of the compartment standing up on edge. One night we had 28°F, that compartment did not fall below 40°F. I got another one and put it in the basement to keep the pipes etc warm. Same results.
Tank heater
https://www.amazon.com/dp/B07ZJMTG7P...ing=UTF8&psc=1
Battery box
https://www.amazon.com/dp/B00EOX2OKS...ing=UTF8&psc=1
Switch
https://www.amazon.com/dp/B09F2WLFHM...ing=UTF8&psc=1
Inline fuse, 7A
https://www.amazon.com/dp/B071ZZNTXY...QB2CJQYB?psc=1