Apple doesn’t want you messing with the iPhone’s battery. Really, it doesn’t. When your iPhone’s warranty runs out, you’ll have to send it back to Apple to get the battery replaced for an exhorbitant fee ($79 + shipping). Yes it sucks, but there’s no other alternatives. Or are there?
In comes Asia, full of OEM batteries and plastic. For only $20, you can get a battery replacement kit for your iPhone that might work. But be careful, ’cause taking apart the iPhone, let alone replacing its battery, isn’t an easy or pleasurable task. Just ask The Boy Genius. He nearly destroyed his iPhone just trying to remove the back cover.