Mine does the same thing, except it's a little different. After it shuts down, I can't turn it on unless the phone is connected to the charger. The battery is fine, though. If I don't connect it to a charger and I check my phone later on, sometimes it'll still be off and other times it'll turn itself on. If it's not connected to a charger and I'm using it, it'll turn off after a few minutes of use. If I'm not using it, though, it stays on. Wth?
At first, I thought it was the battery, but couldn't find anything wrong with my battery. Then I thought maybe it was the screen, but it's not since the phone TURNS OFF everytime. Does anybody know how to fix this?