I can get up to 48 hours out of mine, though I'm a bit obsessive about killing aps when I'm not using them. Turn off GPS and Wifi unless you're using them, make sure you kill any free games you have (they download ads and some of them keep churning away even when the phone is off). Also, kill Dropbox when it's synched - that really drains the power.
Sometimes I can charge it in under 2 hours, sometimes it takes over 5 so you do need to kill anything that you're not using. Also, try and always run it down to under 15% and then charge it up to full in one go - this keeps the battery in good condition. A new phone will also take a few cycles of charging like this before you get the best performance out of the battery.
Also, disable a lot of the bloatware that the phone comes with. Or root it, if you want to get technical, though I've not quite had the bottle to do this myself yet.
"More charges = better life span" and "the battery will get ruined if you charge before it dies all the time" are now nonaplicable to mobile phones as the batteries used are not the same as in the olden days The one thing that kills an S3 dead quickly is if you open a load of apps/internet pages and then go back to the homescreen while leaving them running. Just hold the home button down for a few seconds and close all running apps now and then and your phone's lifespan should grow. It's something lots of people don't realize - you can't close most almost all apps by exiting to homescreen.
I have just bought an S3 after years of iphones. I am loving how customisable it is etc etc but..omg the battery life sucks. It plummets as I watch! It's only making it through the day if I turn all unnecessary stuff off and stop playing with it.
Is this standard for an S3? Will the battery life improve after a few charge cycles? I am thinking of buying an extended battery but they do make the phone bulkier!