Given some of the iPhone 5's other improvements - thinner body, larger screen, and greater number of pixels to illuminate - it wouldn't seem that the new phone could also match, much less exceed, its predecessor's battery life. And, in fact, it doesn't, though it comes close.
Apple has claimed that the iPhone 5 would deliver "up to 10 hours" of video playback on a single charge - the same as the 4S. To see how good the new iPhone's battery life really is, I ran it through our standard battery test and then compared the result to those of the iPhone 4S, and iPhone 4; for good measure, I also compared it to the third-generation iPad and iPad 2.
More specifically, I first updated those older devices to iOS 6. I then took a luminance meter and set the screens of all of the devices to 200 nits. I turned off Auto-Brightness and put each device into Airplane mode. Lastly, I set the volume two clicks up from its lowest setting. Then, with the same 120-minute video playing at fullscreen on repeat, I timed each device to see how long it would take to drain the battery and power off.
The results: Simply put, the iPhone 5 did not last as long as the iPhone 4s or 4. It lasted 8 hours and 21 minutes - about 6% less than the iPhone 4S and about 4% less than the iPhone 4. Compared to the two current iPads (which have much bigger batteries), the iPhone 5 lasted 27.5% less time than the iPad 2 and 17% less than the third generation new iPad.