How to Replace an iPhone battery
Let's face it—batteries are Apple's only real downfall when it comes to their products, and the iPhone is no exception. If you're constantly recharging your iPhone's battery, it's probably time for a replacement (battery, not iPhone).
You can choose to hand it over to Apple, who will send it out to get fixed, leaving you iPhone-less for weeks, and charge you overpriced fees, OR you can buy a replacement battery and do it yourself. This video goes through the whole process of replacing your iPhone's battery, so pay attention and save some money.
NOTE: This is only for the Apple iPhone 1st Generation, not for the iPhone 3G, 3GS or 4.