I was recently approached by a friend who has a Samsung Galaxy S3 Android phone that would go from fully charged battery in the morning and drain to a completely discharged battery by lunchtime (and got physically warm or hot) – all with no phone or app use. Now before you run out an immediately get a new battery, there are a couple of things to check and try.
If you have not yet plugged the phone into a charger, you can check battery usage (menu–settings–battery)…If you see Gallery or Maps or some other application as taking more than 30% and you had not really used the phone, then you probably had an application problem. A quick test and likely fix, is to simply restart your phone, charge it up, and check if the battery life goes back to “normal” and holds a charge.
While this may seem to be a somewhat common problem with Samsung Galaxy S3 phones (most people with an S3 that I know have not mentioned having this problem) I have seen this same problem on other Android phones too. In most cases I have found an app (usually Gallery or Maps) taking up most all the battery, then after a restart, the phone has gone back to normal battery consumption. I chalk it up to an occasional problem where an app loops or keep running, and have not been able to reproduce this problem with any consistency, so I do not believe it to be a case of a bad version of any operating system or version of a particular application.
Updated Tips added 2013-06-24 – Based on all your comments and feeback!
Good luck, and hopefully this helps you enjoy your phone more or support others with Android phones!