I recommend to check battery settings under "change advance power settings".
Check if your "Low battery action" setting is set to 'hybernate' or 'sleep' or 'shut down'?
On my laptop: There is battery icon at right bottom corner of my screen.
I click that battery icon.
Then these are the steps to follow:
More power options -> Change Plan settings -> Change advance power settings -> Battery ->
Then you will see these options:
Low battery level
Low battery action
Critical battery level
Critical battery action
Low battery warning