It seems a lot of people is displeased with the battery life of the new iPhone 4S. Unfortunately, the problem is not limited to the new iPhone users: other devices have been impacted by the problem as well. My iPhone 3GS with iOS5 is almost half discharged after a day on standby. I blamed it on the battery age at first, but many other people have started complaining about the same issue.
I did have a similar issue with my iPhone 3G at some point – when one of the processes kept running on the CPU. This issue looks similar, but is related to Location Services. In iOS5 Apple has divided System Services from other apps, and one of them seems to be the problem – the Setting Time Zone service. If you enable the Status Bar Icon, it will constantly show near the battery icon, meaning that something is using Location Services all the time. Disabling the Setting Time Zone service seems to fix the problem.