How to find out the reason for turning off a smartphone on Android?

Question

Android

A smartphone on android 4.3 (Highscreen Boost II se on Snapdragon 400) often turns off spontaneously. Most often with the Endomondo app turned on (i.e. GPS is active), but sometimes without it. It turns off so that the power button does not work - you have to juggle the battery.
Interested in software that writes logs to files, and what to look for in these logs - the names of functions or some specific system messages.

Answer 1

hard reset