Recently i bought a white iPhone 4S 16GB with iOS 5.0.1 preinstalled.
The phone was running fine for the first week, untill on the 10th day it started giving battery problems. I had turned on siri, puch notifications, locations services, icloud, 3 email accounts, brightness at 50 %. I used to get battery backup of only 12-14 hours with moderate use. 16 though on lite use. heavy use would kill the phone by 8 hours.
Then i browsed the web for sollution, and i got my problem solved. What i did was :
1. Restored the phone to factory settings by selecting " Reset All Content and Settings "
2. After the restore i set it up as a new phone in iTunes.
3. Then i calibrated the battery by fully charging it to 100% and completely draining it untill the phone shut down due to low battery, then i did full recharge again for around 4 hours( my phone showed full charge at 2 hours, but still I charged it for 4 hours).
4. After that i transfered my music, apps, videos, etc
5. I turned off location services ( Main thing responsible for iPhone4S battery drain)
6. Turnned off siri (Siri eats a huge amount of battery while your are using it. And when you are not, it increases the cpu processing to an extent enough to decrease battery life fast)
7. Brightness set to 50% ( Auto-Brightness disabled )
8. Disabled automatic sending of Diagnostics & Usage to Apple in settings.
9. Turned off iCloud. (in my case iCloud eats a lot of battery, even crashed 2 times before)
10. Now the email setup. try to setup as least email accounts as possible, disasble the push notifications, and set update interval to 'manual'. setting up more email accounts sometimes leads to problems in mail app, failing it to properly sync and donwload emails in your phone, causing a bug in background. and the mail app will constantly trigger the process to sync email even though it is not really synchronize. this constantly triggering of mail process eats battery life.
11. While setting up email, after singing in, select only to sync 'emails', do not select calender, notes, contacts, etc. Its better you sync your contacts, calender, notes, etc with your PC/MAC via iTunes.
12. WiFi and Bluetooth turned off. Only turning on when using them.
13. If you use Facebook app, disable push notifications (optional, your choice)
And finally my battery life is awesome now, around 1.5 days of moderate use, heavy use last full 1 day.
Hope this helps.
And remember, if this does not help, then it is 100% sure that you have a faulty battery, so go to apple store and have a replacement.