I get about 16 hours out of my SGS2 battery under moderate use, heavy use tops out too about 10-12 hours.

 

Moved post to the samsung galaxy s2 forum, hope your question is answered quickly

 

It's absolutely normal. On days when I am tinkering with my phone and testing stuff I have even recharged thrice a day. Some days with light use it's lasted upto 30+ hrs on a single charge.

Please do not compare it's battery with a non-smartphone.

Couple of things to note:
Screen is your biggest battery drain.
Talktime (i.e. phone in use) is next.
Bloatware and other apps running in the background are next.

Search through the forum, there are various posts regarding battery on the SGS2.

 

A feature phone (non-smartphone) will go a long way on a battery charge, usually due to a slow CPU/small screen/not running many apps etc....Now that you have a smartphone you have entered into a new realm. Carry a charger with you and/or buy a spare battery. Welcome.