Recently was given an 16GB iPhone 4 from an uncle, running iOS6. The iPhone was given to him by a work partner so history of the phone is hard to track. The phone is operational, everything works fine except it often locks me out stating a temperature warning. Sometimes I need to wait 1 minute, sometimes 5, and sometimes I need to restart the phone to get it working again. The only place the phone feels warm is on the back underneath the rear camera. Also, the backlight is very dim. I have to turn the brightness setting up very high for it to be visible. I checked all 4 water damage indicators and they're all white, so I'm wondering what the issue is. I've been reading around and emailing some repair shops near me and have been told water damage or bad battery, but based on the 4 indicators being white I don't see how it could be water damage, unless the indicators were tampered with. The phone is not under warranty by the way. Any help would be greatly appreciated.