Our LiFePo4 is in a Century Plastics box with an Ultraheat heating wrap around the batt and then some closed cell foam top and bottom of box. I think the temp sensor allows power from the batt to flow to the wrap when the sensor hits 38F and turns off at 45F. We've been down into the teens overnight and the heater keeps the internal batt temp within that range. The power draw is about 1 amp/hr so you have to budget for that.
We've had this system for 3 seasons and it's worked well for us. If you end up with a lithium without an internal heater go to the Ultraheat site and call the number provided. The gentleman was very helpful.
