While on vacation, the phone would just power off for no reason. Would not turn back on, as it thought the battery was dead. I also attempted the reboot (Power button & Down button), but the phone did not recognize any battery available. After about 10 seconds of having the charger on, it would show battery life from about where it was when phone shut down. There was even a time when the phone shut down while just sitting on the night-stand. The first time it happened, I was in the middle of taking pictures. No new APP had been installed recently.
