MacRumors has been pointed to a slew of possible iPhone 5 components, including the battery inside the iPhone 5. According to them, the iPhone 5 battery is pretty much the same shape as the iPhone 4 and packs the same power. Updated.
Specifically, the purported iPhone 5 battery is 3.7v and 5.3Whr while the iPhone 4 battery is 3.7v and 5.25Whr. The iPhone 5 battery was spotted by MacRumors sporting the "DVT_B3" labeling which suggests it's a late prototype. Perhaps power management will be different in iOS 5 but it looks like the iPhone 5 will have a similar battery life to the iPhone 4. [MacRumors]
Update: Wait a second, though. It looks like Kyle Wiens over at iFixit has confirmed that this is actually an iPhone 4 battery and camera module. So all questions about battery life have been just about answered. But! That isn't to say the iPhone won't reuse hardware in some way, as well don't know what'll be inside the iPhone 5's guts. We'll know come October. [MobileMag]