Batteries and very low temperatures don't mix. I have swapped cold batteries for warm ones kept in a shirt pocket in my ZI. Seems to work and the "dead" ones revive after riding in my shirt pocket for awhile.
But I also own a few mechanical cameras that don't like to work when it gets cold out either. It is not just a battery issue.
I understand that Leica used to service their M cameras with different lubricants if you intended to be working in extreme low temperatures.
I have also heard of problems with film in sub-zero temperatures but have not experienced any problems myself.
You gotta love a fast lens;
It is almost as good as a fast horse!