In reply to ecrinscollective:
Thanks for all the advice gang.
I guess I will have to do a bit more digging, I understand that an newer Iphone or similar is a far better phone to use, but battery life really worries me, a few friend have them and the don't seam to last a day tour in the cold even with very little use. A few end up having to carry a powerbank which I guess is an option, but feels like buy an more expensive phone a case and powerbank, when something else does it better.
As for using it during the day and needing it for emergency calls, it looks like a tougher model that is cold resistant should do that for a day tour, I'd use it to nav as a quick aid but always carry a map, and for photos often have a bigger camera in the bag if I can be bothered to get it out, so guess my thinking is if i notice the phone losing charge a lot in the day, I can put it away and use other things.
May see which mate are getting an upgrade and go for another hand me down to get me through.
thanks again