Jess, you and I have some similarities when it comes to work and photos for documentation. I suggest NiMH rechargables for most circumstances, along with a car charger, and lithiums for those really cold days or as back-ups to the rechargeables. I think that you want to stay with a camera that uses AAs, rather than some proprietary battery that's going to leave you hanging in the middle of nowhere.

The other thing to check is the memory card. Some of those are remarkably intolerant to cold, but they do make "extreme" cards.

On cold days, I keep my camera (and pens!) inside my Carhartts to keep the batteries and zoom lens happier. It's not ideal, but it's better than nothing.