Ive had a similar issue but my phone will have more than %20 battery and just shut off. Sometimes it has as much as %67 left. Then it won't go past the splash screen till i plug it in. When it does turn back on sometimes it has the same amount of battery and sometimes it says that it has 0. Is there any way i can check if this is my battery just being dead or perhaps it needs to recalibrate or something.