Mine is an old Circuit City fixture; I bought it for something like $5 a couple days before they completely closed up. It had a dead battery, but I had a few 12v lead-acid batteries around. I cut the original divider plastic out of the battery compartment and now it has twice the capacity it did when it was new!

It's an APC Back-UPS 350, and it keeps my computer, monitor, clock, and Ethernet switch going when the power goes out.
I've got an old APC Back-UPS 500 on the TV and DVD player, too. The battery doesn't last quite as long as the good one, but it's a decent surge protector, and it's enough to run a lamp and keep the standby memory in the devices going.