I have been using Samsung GS2 for six months and recently been suffering from severe battery drain. I would get just 8-9 hours on a full charge with very light use.
Went through the Internet and searched forums and finally hit jackpot.
Here's wht I did:
1. Calibrated the battery. I let the battery drain completely and allowed the phone to automatically shut down. Then charged the battery from zero till 100 per cent.
I did it three times over a week.
The last time I did this, once my battery was 100 per cent, I removed the battery, waited for 5 minutes, reinserted it and switched on.
2. Turned location services off
Go to Settings, Location services:
Untick Google's location service
Untick GPS satellites
Untick Location and Google search
(Unless u r using Google Navigation a lot u dont need these)
3. If u want to desperately save battery life...
Turn Auto Sync off:
Settings-Accounts and sync
Turn it off
4.Turn wi-fil off during sleep
Settings--wifi--Advanced (menu key) Keep wi-fi on during sleep ---Never
These steps hve worked for me, especially the first two, hope u guys will find them useful.