Are you using an unofficial battery. My phone did that when i used a unofficial battery so i just changed back to my old battery

iKier wrote For some reason when my S3 goes below 15% the screen starts flickering then eventually it freezes and my phone dies on like 12%?
Anybody help?

Hey man, I had a Huawei Ascend and that done almost the same thing. The phone froze for about ten minutes then the screen turned off and wouldn't turn back on till it was fully charged or at least had enough charge to get back up andrunning, so me and my Dad opened the phone, it was the connectors that were falling off a bit and we replaced the battery then it was working fine. So I'd advise sending it away to get fixed/checked out.