Hi,
I had the same problem but i think that it's fixed now, still have to test it...
I turned off everything possible like most of the guys on this forum, most of the thing were unnecessary anyway.
---------------Here is the list-------------------
WiFi turned when not needed...
Settings-> Notifications (for most of the apps)
Settings -> Location Services -> System Services -> Compass Calibration
-> Diagnostics and Usage
-> Location Based iAds
-> Setting Time Zone ---- seems very important to turn off
-> Traffic
Brightness set to Auto-Brightness...
General -> About -> Diagnostics and Usage - DON'T SEND
General -> Siri -> Raise to speak - OFF
Bluetooth - OFF
iTunes WiFi Sync - OFF - This should be uncheked in Itunes when connected to a computer
General -> Restrictions -> Ping - OFF
General -> Date and time -> Set Automatically - OFF
Mail, Contacts, Calendar -> Fetch New Data -> Push - OFF
Mail, Contacts, Calendar -> Fetch New Data -> Fetch -> Manually
------------------------------------------------------------------
After turning that off, battery life was slightly better, but not even close to the expected...
But the biggest problem was Usage & Standby time were the same, and according to that, it seems that the phone is never actually in standby mode.
Next i did was:
Remove existing email accounts
Reset Network Settings
Reboot the iphone (By holding the sleep and home button at the same time until the Applelogo appears)
Create email account again
And i think the most important(I FOUND OUT ABOUT THAT LATER ON):
Mail, Contacts, Calendar -> Fetch New Data -> Advanced-> Manual for every account
I don't know what exactly did the trick but when i charged my phone to 100% it stayed like that for the next 3,5 hours which i couldn't imagine before...
I will keep it on very light usage to see how long will it last and then will try to turn on some settings one by one.
So far, so good...

Hope this will help you...
Thanks.