I was planning to use my old iPhone 3GS for weekend project but I discovered that the screen was popped out and the back was bulging, I took it apart and this
The Second Coming: Ars goes in-depth with the iPhone 3G | Ars Technica
File:Expanded lithium-ion polymer battery from an Apple iPhone 3GS.jpg - Wikimedia Commons
iPhone 3GS Battery
Maximize The IPhone 3G's Battery Life | Hackaday
iPhone 3GS / 3G Dock and External Battery Pack
How to Enable the Battery Percentage on iPhone 3GS « iOS & iPhone :: Gadget Hacks