unexpected shutdown and bios reset when there's no charger connected

[zatyji]

I have an Asus X540YA (a cheap laptop, bought less than 6 months ago). I have dual boot Windows 10 and Elementary OS installed on it. Now, when it is running on battery power (not plugged in), it unexpectedly shuts-down in both OSes (though, it stays alive a little longer on windows than on elementary). It even goes as far as resetting the bios automatically (I noticed this when I saw the bios time is reset to 0:00:00 and puts Windows Loader as default, instead of grub). This issue started just a couple of months ago.

I tried to check for hardware for errors and everything pointed towards the battery, but running

acpi -b

shows that battery is fine. Thermal's look good too, around 58deg. Please let me know what I can do to fix it, as it is still under warranty. Thanks