Very awesome Thanks for sharing. What'd you do for power? Was that on just the 2 batteries in the grip? They lasted the whole 6 hours of continuous shooting in that cold? Wow!The 1DX only takes a single battery, and it is different from the batteries in the 5D's (maybe someone here can explain what makes them different as I'm not entirely sure). I was worried that the cold might zap it a little quicker, but it held up just fine. At the third hour I swapped out for a fresh one, but there was still a bar left.
1D-series use 3 cells in series (~11V), compared to 2 (7.2V) for others. In terms of mAh, the higher voltage gives 50% more capacity in theory, but if you calculate energy density, it comes to same number. So it's all about volume, and 1D batteries are roughly same size than 2 "standard" batteries, thus giving roughly twice the capacity compared to one normal.
Cold hurts batteries, at ~-15C (~0F) you typically get only 50% of the nominal capacity.