I faced a similar problem, this is what you should do.
1. Check the current firmware, I think you must be on KE4
2. Connect to samsung kies, see if any update is available(In my case, samsung kies said no update available)
3. Google for KE7 firmware and download it. Make sure it is for your region.
4. Use odin to install it, plenty of guides out there. (This is not rooting, or installing custom ROM..its just normal firmware upgrade)
You should experience much better battery life.
You can connect to kies and find the next new firmware and update.
Remember to backup all your data before doing this.
Some more tips for better battery life :
1. Dont use live wallpaper.
2. Keep the brightness to a low level.
3. Turn OFF the automatic brightness thingy..it doesnt help!
4. If you want to go extreme, change the wallpaper to a complete black one.
Hope this helps