About half a year ago I bought a used UPS. It didn’t have enough output to power my main PC, but it’s perfect for my home server and network.
Starting on Christmas eve and continuing even today, my neighbourhood has been getting intermittent brownouts. It’s only affecting one phase (house is on a three-phase 240V connection), which happens to be the one powering my network (also all of the light fixtures, stupid Soviet house), and the UPS works beautifully. I didn’t lose any of my services even once. Without it, I would probably be reinstalling Proxmox and praying to the RAID gods to restore my hard drives.
“It pays for itself as soon as it is needed” is proven true once again.
I have a 12V 200Ah battery sitting outside in the rain next to my car parking spot. I got it for free (It used to belong to the emergency power bank of a ship, but it was swapped out). Now it’s mine “just in case”. It has saved me a couple of Icy mornings when my car needs that extra boost. I also ran my routers and switches on it once during a power outage, as I have a 12V to 230V inverter available. 200Ah goes surprisingly long.