I have two 12v 9AH Stark LiFePo batteries. On their website it gives –20°C to 60°C (–4°F to 140°F) as operating limits and a charge temperature range of 0°C to 45°C (32°F to 113°F).

The capacity graphs for 25, 0, -20, -40 C ( https://starkpower.com/product/12-volt-9ah-battery ) tab at the bottom shows they're good batteries down to 0 C, but perhaps a poor choice for the real cold.

This explains the voltage drop in the Lake Placid wave... I will have to put a voltmeter readout in for the next camp. I remove the batteries for charging.