UPS ?

[Mike Watterson]

The battery is a 12V 7.2 Ah. So wont power anything for very long.

Sounds like the standard 12V SLA Gel pack. It's purely to run a PC or small server long enough to save work and shut down. I have two such UPSes and the battery packs need replaced every couple of years. One is on my small server and network gear and the other on an Optiplex mini-workstation & 4k screen that replaced my laptop as I don't go anywhere. Laptops have the advantage over "All-in-one" PCs (that are often laptop like MoBos) of having a decent built in "UPS".

Some UPS boxes can be adapted easily to use a small car battery giving about x5 to x7 run time.

It's sort of fashionable now for solar systems and UPS to have Lithium batteries, but the advantage of Lithium is purely low weight for cars and tools. The Lead acid is safer, cheaper, 100% recycled and weight is no issue for Solar power or UPS systems. Serious solar power has inverters driven by panels (Nominal up to 45V) to charge 48V nominal batteries (as car is 14V approx charged, they are 56V fully charged). Then the 48V battery system drives inverters to give AC mains. There may optionally be electronics to feed the grid and/or smart charge the batteries. Some solar systems save money by having no batteries and only feed grid excess power. A decent set of batteries costs more than standard panels.