I've been testing the iPhone 5 for 10 days now. The iPhone 5 ships with iOS 6 installed. I've found that the battery life continues to be very good, given all that the device offers. Keep in mind, it has larger display, a faster processor, and a more power-hungry LTE 4G radio on board.
Combined, these might have been a disaster for the iPhone 5's battery life. Instead, the slightly larger battery in the iPhone 5 and the way the A6 processor handles iOS 6 means excellent power management. Obviously, mileage with something such as battery life of a smartphone will vary greatly depending on how the device is used. With the iPhone 5, I've kept the Wi-Fi radio on at all times, have the screen set to about 50% brightness, and use it quite consistently to change social networks, email, take/share photos, and so on.
So far, it has exceeded my expectations. It easily lasts an entire day, from early morning to late evening. I generally unplug my devices from their chargers at 7:00 or 7:30 each morning. Even on the days during which I used the iPhone 5 intensely, it was still registering more than 30% battery life remaining after 11:00 in the evening. I have yet to put it through a torture test (i.e., spending a day with it at a busy trade show). That'll come soon, though.
But iOS 6 isn't as friendly to the iPhone 4S and iPhone 4 when it comes to battery life. I've installed iOS 6 on both the iPhone 4S and 4, and, have noticed, along with other users, that battery life has taken a pretty big hit on these older iPhones.
I have the same basic set of applications installed on the iPhone 4S and 4 as I do on the iPhone 5. The important ones--email, Twitter, Facebook, and others that ping the network regularly for updates--are all identical. With Wi-Fi on, but cellular data turned off on the 4 and 4S, neither device lasts 24 hours any more. They used to--and still should--last several days at a minimum.
Something in the way the iPhone 4S and iPhone 4 are interacting with iOS 6 is causing excessive power drain.
For me, this isn't that big a deal. I no longer use the iPhone 4S/4 as daily drivers. I have the iPhone 5 for that. But for the millions of consumers who have stuck with their older iPhone hardware and updated to the latest system software, it's an important issue.
Have you updated your iPhone 4S or iPhone 4 to iOS 6, and are you seeing diminished battery life? Please feel free to sound off in the comment below about your experience.