I have a new to me iphone 5 and I travel to the US a lot. I've noticed that in Canada my phone is perfect but in the US the battery drains super fast. It will go from 100% to dead in 4-5 hours. In Canada it lasts 2-3 days. I often see it display 'no service' in the US and am wondering if maybe it is constantly searching for Canadian towers? It is locked to the telus/koodo network, my last phone did not have this problem and was unlocked, could the lock be the issue?