Robin2:
Or what about a cheap laptop that only has SSD storage? - comes with in-built UPS.
I use to use old netbooks with a broken panel. Remove the panel, fit a small ssd, install linux with VNC viewer or XRDP. You access them remotely from a main computer just when you need it, else they run 24/24/365 with a very low power and have backup for half a day...