Short answer: most LiFePO4 batteries can discharge well below freezing but should not be charged below about 32°F (0°C); many BMS units block charging there. Self-heating batteries warm themselves using charger power first.
Ways to keep lithium batteries warm
Mount the battery inside the heated living space, not in an outside compartment.
Use a self-heating LiFePO4 or an approved heating pad controlled by the BMS.
Insulate the battery box (leave ventilation per the maker).
Charge in the afternoon when the battery is warmest; solar then has the best chance.
Watch battery temperature on a Bluetooth BMS or monitor.
FAQ
Can you charge LiFePO4 below freezing?
Not safely in most cases. Charging below about 32°F (0°C) can cause lithium plating; most BMS units block it. Self-heating batteries warm the cells first.
Can LiFePO4 be used in cold weather?
Yes, discharging is usually fine well below freezing (often down to about −4°F), but capacity drops in the cold.
Why isn't my lithium battery charging in winter?
The BMS low-temperature charge cutoff is likely active. Warm the battery and charging should resume.
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.