My cellphone turns off randomly and hardly turn on again

[AC Question]

I have a Nexus 5X since February, it worked fine until Friday (10.28). Suddenly it has restarted and it keeps booting. Once in a while the boot works and the cellphone starts working, but at some point, randomly it turns off again. I tried to factory reset but I can't because I don't know when the cellphone will work again.

 

[belodion]

A failing battery? A poor battery connection? A faulty power switch?