Hello Adamis,
I also have a Bigfoot Camper 25c 9.4 and am going through the process of gathering all the information I can regarding Lithium Batteries. On my camper the "Battery Box" enclosure is a plastic box with a vented metal door on the outside of the camper. The BB is located directly under and behind the sink cabinet with an open (at the top) partition separating the two.
Here are my suggestions for your situations.
1. Insulate the access metal door with poly iso foam board - cheap at R 6.5-7/in. fit it very tight. Now it will be inside you conditioned space.
2. Keep cabinet doors open during the night to allow heat to circulate into the cabinet area. If your set up Is similar, remove the partition to allow more air to circulate around the BB.
3. Only use the inverter portion of the inverter/charger during times you need to warm baby bottles or make coffee, avoid using the converter for convince i.e., microwave, AC outlets, etc. Note: baby bottles have been warmed on the (propane) stove in water and tested on the wrist for decades, use an accurate digital thermometer if you want to go hi-tech.
With the above low cost measures, you should be able to: have more usable Ah in the battery and keep the Battery warm for very little time and expense.
Congrats on the baby girls. Enjoy and safe travels.
