According to Haslam, a feature on iOS 5 that keeps the local time on the Apple iPhone 4S correct-even when the user might have switched time zones-is apparently responsible for the battery drain on the handset. The good news is that the "Setting Time Zone" function can be disabled which would allow the battery to power the phone for the expected length of time. The price to pay seems rather small as Apple iPhone 4S users would only have to remember to manually change the time on their phone when traveling to a different time zone.
Apple iPhone 4S, the Apple iPhone 4 and the Apple iPhone 3GS. He blamed the problem on a bug in the software that caused the location tracking circuitry to constantly check with cell phone towers to determine the location of the phone. The program uses the signal from cell phone towers and triangulation to get a fix on a current location. The feature is supposed to check in only occasionally with the towers to find where the handset is located.
Apple's own testing has allowed the company to claim that the newest version of Apple's smartphone has one more hour of 3G talk time than what is expected from an Apple iPhone 4. A test done by CNET using a Sprint branded Apple iPhone 4S resulted in 9.2 hours of talk time over the carrier's Ev-Do Rev. A 3G pipeline. The battery in the Apple iPhone 4S has an extra .05WHrs of power as compared to the cell on the prior version of the phone, according to a tear down of the device by iFixit.
source: iDownloadBlog, TheGuardian via CNET