I am having the same issue with battery... phone switching off at 15%, even at 22-23%, when playing a game or something. But switching it back on, and leaving it idle, phone might run for another 2 hours. So it is the extra load while running a game that the phone cant take any longer (i remember getting the 15%,10% and 5% reminders earlier while playing games)...? Does the battery calibrate method actually help in your case? does it go all the way down to 0% or 1% before shutting down.. ?