Some users are still having issues with poor battery life even after installing the latest iOS 5.0.1 which was supposed to fix battery drains. Even more, certain iPhone 4S owners are reporting worse battery life than before the update.
However, according to some lab tests, the battery issues on the latest Apple-phone are not hardware related. Restoring a backup from a device having battery problems to a similar device that runs fine and vice versa proves that the problem can be “ported” to another device (and the one with the problem can be fixed). This means that the battery problems are not due to hardware but indeed are caused by software. You can read more about the setup by following the source link.