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
100% NEW battery for iPhone 3G 3GS within tracking number| | - AliExpress
Battery Upgrade Kit - iPhone 3GS Repair and...
Official iPhone 3G / 3GS Battery Replacement Video & Instructions - iCracked.com - YouTube