I found the battery life pretty bad too but I did find it improved slightly when I flashed the firmware to a stock firmware instead of the Optus one. This got rid of the Optus start up screen, Optus apps and any other changes they'd made to it.
Also if its the LTE version you can turn LTE off and just use 3G. That alone will improve battery life.
I have to say though the iPhone 5 I have now, even with everything turned on, lasts double the time what my S3 did between charges. I was charging that by midday after taking it off charge around 6am. I take the iphone off at 6am and put it back on late that night at bed time (11pm or later) even then there is still at least 20%+ left on the battery.
Edited by SummerStar, 15 December 2012 - 05:42 AM.