Internal UPS for desktop computers? [closed]

I was wondering, are there internal UPS'es available for desktop computers?

Every laptop has something like a UPS in it: The battery pack. Desktop computers don't consume that much power, it should be possible to integrate a battery pack, that is able to fully supply the computer for say 20min. The idea is to have the battery pack behind the PSU, so it would power the mainboard and drives directly, and not through the PSU, as conventional UPS'es do.

To put it simply: Port the convenience of laptop computers to their desktop counterparts. Since there won't be too many users using their desktop computers from the battery alone, this would only serve as UPS, and let the computer running for no more than 20min or so, just enough to skip small outages without shutting down, or safely shut down the computer after a certain amount of time.

I don't believe I'm the first ever person to state that idea. Is something like this available? And if yes: Where? Conventional UPS'es would be then sufficient to power the monitor and other periphery, like network switches, etc.

As a side note: I've seen a lot of people putting much effort in securing their servers with UPS packs, but not powering the network parts with a UPS. They've lost all connectivity to the servers on an outage, the servers just went powerless once the batteries died.

There used to be a few 'battery cards' on the market some time (>>5 years) ago that plugged into an ISA slot but I haven't seen sight of anything like that recently, but you can get units that fit into a standard 5.25" drive bay - do a Web search for "PC Internal UPS":