do mean you are using it and browsing for 10 hours straight ? Then that sounds about right. if you mean just on standby with the screen off for 10 hours then that would be a problem.
Most battery problems can be traced back to as follows;
dodgy battery – buy a second battery with external charger from ebay (for a reasonable price you should get a genuine one) and see if it is improved. this also gives you a spare charged battery to keep with you for long trips too. I’ve heard even some of the genuine ones have problems and have been replaced by samsung
battery bedding in – it might take a while for a genuine battery to get a proper charge. Give it a few weeks and see if it improves.
Version – Even early versions of ICS (even up to 4.0.4) were very crummy. I’m running PDA:LQR and its very much improved. 5-10% drain overnight in standby mode. It still chews the battery when in use.
Apps running in the background not allowing sleep – Check the blog post on this site on how to install some apps to troubleshoot which app is stopping your phone going into sleep. usually only a problem if you are getting charge loss when the phone should be sleeping
