An Apple iPhone 4S displays poor battery life, approximately 10 hours standby time compared to the 200 hours in the specifications.

Under Settings | General | Usage the reported usage is around half of the standby time, even if the phone hasn't been used.

Performing a Settings | General | Reset | Reset All Settings and setting up as a new phone, or a Settings | General | Reset | Erase All Contents and Settings then restoring from iCloud does not resolve the issue.

As an initial step, remove all email accounts and monitor battery utilisation. If this resolves the issues, add the email accounts back, otherwise follow the steps below.

There is a known firmware corruption issue with iOS 5 that causes this. The only current solution is to install a a fresh copy of iOS, set up as a new phone and NOT restore from backup.

Reload the firmware using recovery mode and iTunes.

- Put the phone into recovery mode: http://support.apple.com/kb/HT1808
- Plug the phone into iTunes and follow the prompts.
- Set up the phone as a new phone.

Do NOT restore backups, as this will reintroduce the issue. You WILL lose all application data, but items in iCloud such as Contacts will be preserved.

iOS: Unable to update or restore
http://support.apple.com/kb/HT1808