My girlfriend recently got the AT&T GS3 and was having big battery issues - the battery was constantly hot and the phone was constantly draining fast and would be done in 4 hours. Personally I don't believe people should have to solve this issue with gimmicky crap like turning data off when the phone sleeps, setting the brightness so low you can barely see things, etc. The phone battery is designed to last a day+ with normal use, so issues like the battery crapping out in 4 hours point to something deeper. I took a look around and found the following:
(I can't post the link but it is an ATT forums post called "Samsung Galaxy S3 Battery Drain (sudden drop)" and the steps are on the second page)
I followed these steps from user "erickb1800":
There was no Samsung Account under Accounts & Sync so I did not have to delete that. But I did disable those 5 apps listed in step 3 and it basically made the problem go away. One of them was using CPU constantly in the background (it only showed up as "Android OS" in the battery page tho) and disabling them seems to have solved the problem.
(I can't post the link but it is an ATT forums post called "Samsung Galaxy S3 Battery Drain (sudden drop)" and the steps are on the second page)
I followed these steps from user "erickb1800":
1. Go to Settings - Accounts & Sync. DELETE the Samsung Account (you don't need it)
2. Go to Application Manager, and select the ALL tab.
3. Scroll down, and then STOP and DISABLE the following; Samsung Account, Samsung Backup Provider, Samsung Cloud Data Relay, Samsung Push Service, and Samsung Syncadapters.
4. Exit out, reboot the phone, and your battery drain should revert to normal. Immediately following that, I have lost 20% of my battery with normal use (including normal Sync for work and Gmail, etc) in the last 8 hours.... I am back to utter contentment with my S3.
There was no Samsung Account under Accounts & Sync so I did not have to delete that. But I did disable those 5 apps listed in step 3 and it basically made the problem go away. One of them was using CPU constantly in the background (it only showed up as "Android OS" in the battery page tho) and disabling them seems to have solved the problem.