One thing that you can do is keep spare batteries in your pocket, as close to your body as possible. Cold temperatures limit the performance of a battery but don't actually drain it. If your battery dies on the mountain, take it out, put it somewhere warm for a few minutes (like a close pocket) and put it back in the camera - you'll get a lot more time out of it.
By the way, this trick also works for cell phones, too. If your cell phone dies somewhere cold, put it's battery somewhere warm for a few minutes and you should be able to get another phone call out of it.
