I was in Yellowstone last Feb and Nov, extremely cold temperatures from -10F to 20s and was out for 6-7 hours. First time I had a T3i with me, second trip had a 1DX. I went thru 3 batteries on the T3i for may be couple hundreds of pictures. The 1DX battery had no trouble for the whole day.
Unless it is snowing, there is no issue with condensation when your gear going from warm to cold. I changed lens with no problem.
Going from cold to warm, I left my gear in a Lowepro 500 bag and let it gradually warmed up to the cabin temp. We turned off the cabin better when we went out, so when we came back it took time for the cabin to warm up. I did not put my gear in zip lock bags and it did seem to have any condensation issue. The point is to avoid bring cold gear to warm room suddenly.
I wore a mitten with inner lining that I could keep warm when not shooting. This was the ardent part. And keeping my feet warm. I wore Baffin boots, the kind people wore to Antarctica