Samsung Galaxy S III might have a software bug draining its battery
Samsung has yet to acknowledge such a battery bug, and we cannot confirm its presence either since our Samsung Galaxy S III seems to be working just fine. Yet those who have researched the matter in detail claim that a value in a system file is causing all the trouble. As a result, the amount of power that is being used when the smartphone is in stand-by mode is about 10 times greater than it should be.
Now, if you have a U.S. variant of the Samsung Galaxy S III, don't worry as your handset is not affected. But if you own the smartphone's international version, and its battery life is not as good as it should be, you might want to head over to the XDA-Developers forum and check out what the guys have to share on the matter. Should you have the skills to resolve the glitch yourself, we cannot stop you from doing so. It would be much wiser, however, to simply wait until an official update squashes that battery bug.
source: XDA-Developers via Android Authority