When the battery gets low enough to automatically turn the phone off, you're killing it. The normal turn-off point is around 10% to 20%, and you should NEVER let the battery get below 40%.
Welcome to Android Central! Can you describe more in detail about this "auto power off" problem? Is it shutting down on its own when the battery is still well above 50%, or is it really low (as Rukbat was addressing)?
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