Even im having battery problem on Galaxy S2. Kernel: 3.0.31-siyah-s2-v6.0b4+.
Usage: daily 1-2 hours of music listening, 1-2 hours of chatting on different messengers, internet surfing.... but that is very less often.
My internet data network is ON every time. I use to get very good battery on 3.6.28 more than 20 hours every time!.... but since new versions are getting released... I haven't re-installed that version and checked.