Solved! Acer Aspire won't start windows. Battery or more serious?

Jun 9, 2020
I have a 4 year old Acer Aspire F5-571with a reasonable (Core i5 8Gb/1Tb) spec. It has had little use as it is a spare in an office.

Now it resets after opening the Windows login page. It is a little random. Sometimes I can actually enter the password and then it shuts down, sometimes it shuts down before I get that far.

I thought it might a battery issue, but it is plugged into the mains and the charge light is on so I know it has power.

What puzzles me is that I can load the BIOS page on booting and this remains active for over an hour without an issue, making me think that it is more than just battery. I have tried removing the mains power whilst in bios screen and this does cause it to shutdown so the battery is suspect.

What other diagnostics can I try or should I just get an expensive (£50) new battery?
check the memory by running usb autoinstaller (bootable USB flash drive)

boot with windows install disk/usb flash drive and try repairing windows with it
could be a hard drive fault as well