In reply to Kat4kgb:
Do you need an emergency phone or a phone to use it frequently on mountains? I usually have a smartphone with myself, but it is mostly useless and I keep it turned off. I have a Nokia 100 (105 is a better model, though). Its battery is supposed to last 35 days (lasts at least 20 days if not used). If you keep it in inner pocket of your jacket, it would work.
The best thing is that Nokia 100 costs about 10 pounds. I did not even bother looking at shockproof phones. If I ever happen to break it, I can buy another one. And the phone also has a torch, which is not very bright.
The main thing with most of batteries is that if they get cold, they do not work. When I was at school, I have seen many peers rubbing their dead batteries into their jeans and "the battery charged", as they said. To read more, check this link:
http://chemistry.about.com/od/howthingsworkfaqs/f/coldbattery.htmPost edited at 22:19