For starters never restore it as new as I've seen people on forums suggest. That deactivates it from the carrier and then you have to reactivate your number and everything secondly have you done a hard reset while it was plugged in? Because they could have messed up the sensor that reads have much power is left. Thirdly check your usb cord if its falty it could mess up your phone's ability to hold a charge. Take it to an Apple Store though instead of listening to forums though