I use my old iPhone 3GS as an iPod/Pandora player in my studio. One morning I came in and discovered that the iPhone was swollen like a tick! The back was distorted and the glass on the display was pushed 1/4" off the front of the phone. I guessed that I had a major battery malfunction going on. What's crazy is that the phone still worked!
When I was finally able to get the display assembly off (which was complicated by the fact that the glass had separated from the rest of the assembly) I could see the mother board was all distorted from the pressure of the expanding battery beneath. The screws nearly shot out as I was removing them! But I got all the connectors and screws removed without incident. the photo shows the bloated battery in the phone, and the new battery next to it. Anyway, got everything back together and the phone is like new!
Mind the process for removing each microscopic connector, and keep track of which screw is which as you remove them.