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
iPhone 3GS cracked open b/c of bloated ba… - Apple Community
Several backup batteries can extend your daily iPhone 3G use | Ars Technica
5-Pack of Batteries for Apple iPhone 3GS 8GB 16GB 32GB 616-0431 616-0434 616-0433 A1303 A1325 NEW