Compared to the One X the battery life on my S3 is night and day. Quite literally
Still I always carry a spare and with the pair I can easily manage 15+ hours of internet/music/video consumption which is plenty for someone who needs a decent amount of sleep. With light usage it lasts 4 days.
I'd take a look at what's sucking the battery either in battery details or with an app like System Panel App that tells you the exact CPU consumption of every application. Then Titanium Backup to disable the sucky ones