While I live in a moderate climate, officially, a temperate climate, I have the Nikon DB-2 cold battery pack unit. I picked this up in Germany on a very cold January day when I visited a camera shop to buy new batteries for my Nikon F3 body. I had been out in a forest around 1,000m high for a couple of days in temperatures down to -20ºC taking pictures of frozen trees which were covered in a layer of ice a few millimetres thick, due to an unusual weather phenonom that caused rain to happen between 1,000m and 1,500m which instantly turned to ice when it came into contact with the very cold trees. Sounded like a crystal chandelier tinkling in the wind.
The extra battery pack worked a treat and on the odd occasion I have ventured into quite cool environs since, I've always ensured I have it.
The only issue I have is that the lead could be a bit longer, allowing me to have it inside my down jacket and coming out of my sleeve. It isn't long enough for that, so it comes out in the middle of my torso. With extreme cold and a lowish battery set in the camera body, I found that vertical shots worked one way, but were audibly slower the other way, horizontal shots were not seemingly changed. It was only a short time after noticing this shutter difference, that the batteries would die.
I tried Lithium batteries, but they died instantly, I prefer the more normal battery type that starts to die in a controlled and noticeable manner, this allows one to seek shelter to somehow replace batteries. As for dropping button batteries in the snow; best excuse for getting an external battery pack.
Mick.