The amount of bloatware preinstalled on the phone is insane, and TouchWiz is a real battery hog. I recently installed Cyanogenmod on mine, and I can easily get 15 hrs out of it without tweaking it whatsoever. If you're more of a tweaking type, you can downclock your processor and install screen filter (it darkens your screen lower than what is allowed though android) and get around 2-4 additional hours out of it, depending on your settings of course.