Comment # 17 on bug 985741 from Richard Brown

(In reply to Bj�rn Lie from comment #16)
> sudo vi /etc/UPower/UPower.conf
> 
> CriticalPowerAction=HybridSleep
> ==>>
> CriticalPowerAction=Hibernate
> 
> sudo systemctl restart upower.service
> 
> Let system run out of juice.
> Does it still reboot?
> 
> I have a strong feeling a lenovo x1 I had in the past, was bios hardwired to
> wake up when reaching a certain low level of battery while suspended so that
> windows could then put it into hibernate.

This is confirmed on my ASUS i7 UX303LN as well as Stathis' ancient celeron
compaq laptop

So I don't think it's hardware related

Still think the above is a good test, Stathis can you try it? :)