iPhone 4s, justover 12 months old, crashes in cold

My iPhone 4S is just over 12 months old. Last November , whislt out cycling, I had the phone in my inside pocket and as soon as I took it out to use it, the phone crashed. Temparture was around 10 degrees C.

Since then, the phone very regulally crashes as soon as I take it from my pocket, into the open air. It looks like the battery needs recharging, however once the phoned is warmed in an inside pocket, it works again and the battery will show 75%.

Having moved from a Blackberry 12 months ago, this is starting to become a big problem.

Any thoughts, solutions?