I don't know about Lithium batteries, but lead-acid ones have an interesting thing where their freezing point is much lower if they are fully charged. The acid

I don't know about Lithium batteries, but lead-acid ones have an interesting thing where their freezing point is much lower if they are fully charged. The acid concentration is higher and works like antifreeze. If you let it go flat the concentration drops, and the physical expansion from the water freezing just destroys the thing.