Originally Posted by travelingaustralian
I just keep them in my jacket pocket close to my body. I have 2 batteries for my camera and replace it with the one in my pocket. I then put the flat battery in my pocket as it warms back up it gets more life into it. If im doing time laps i cover my camera with a t shirt then use heat trace wrapped around it that I can plug into a power point.
Wow, is that enough? I've been trekking high altitude and in cold weather (not as cold as yours!), but have always been unsuccessful at having batteries retain their charge.