Use handwarmers...

[casil403]

....to keep spare batteries warm in cold weather! Works great in frigid temps!

[AcadieLibre]

I wear tight mechanic gloves under a good set of leather mittens with kiddie strings so I can just drop it off my hand and I don't lose it. Hand warmers are something I think is always a good idea to have with you anyway, a set for your hands and a set for your boots if you start getting to cold.