Some SGS2 / Android owners has to fight with battery. I flashed the I9100XWKE7 firmware and still have bad battery life. After rooting it I decided to remove strange services and background applications. To do it install a root uninstaller app; now has been removed from market, but you can find it easly elsewhere.
After removing a lot of unuseful packages such as wallpapers, “Ap Mobile”, strange widgeds, Yahoo Finance, I decided to remove Wifi Sharing and Wifi Sharing Manager.
The Kies Hospot is still working, no problem and the battery is lasting almost double. Just pay attention to TwLauncher, Android need it to start.
It is a good idea if you dont like to flash new firmware so often.