Just a personal experience: I had bought several ~$20AU iPhone 4S batteries from eBay from different sellers, and while they started off okay their capacity dra

Just a personal experience: I had bought several ~$20AU iPhone 4S batteries from eBay from different sellers, and while they started off okay their capacity dramatically decreased after a few weeks. Also I'm unsure on how a device determines battery charge, but I forever had issues with the phone turning off while reporting the battery had ~30% left. Maybe I didn't treat the batteries correctly, but I can't recall as this was several years ago.