High processor/CPU load on iPhone, draining battery, how to fix?
Do you use Exchange on your iPhone? At our company we have some trouble with contact sync every once in a while. Various iPhones will run at 80% CPU and their batteries empty in about 2 hours.

One temporary fix is to turn off contacts in Exchange Settings and turn it on again. Then contacts will be sync again and after this CPU runs at a normal 5-15%.