Another option is just to use an old laptop. This is what I tend to do for media servers, TV computers, and the like. People give away or throw away perfectly usable machines all the time.
I used to do that for my media server/HTPC. The problem in my experience is that laptop fans are pretty noisy. Actually evenn the power supply can be noisy, many of them have a very audible AC hiss. Maybe it's because I tend to buy cheap laptops.
A few months ago I decided to build myself a super quiet replacement, I took a small well ventilated case[1], put an underclocked i3 in it, a fanless heatsink[2] on top, a super quiet power supply[3] and it's amazing. For about 350 euros I have a completely silent and rather powerful HTPC. A lot more expensive than the computer in TFA obviously, but well worth it if like me you can't stand fan noises.
I'd imagine it be prudent to remove the battery if that is the case (which you can't on many newish laptops). I know it's tempting to utilize that free UPS but I wouldn't trust a laptop battery that's pushed way passed the intended use.
I did use a laptop that way, and I think that I did knacker its battery prematurely, though I'd simply these days be more gentle about switching between it and external power, like I do with my network gear switching between mains and off-grid.
Is "pushed" the right word? Rather it seems like the battery is not doing much apart from a little "ambient" discharge for which it occasionally gets automatically topped back up to 100%.
For the plugged-in laptops I use as servers, I have a repeating task in my todo system to unplug and drain them once every couple of months. The intention being to keep the thing's own idea of its calibration honest, in case it ever gets used like a normal laptop again.
Well, I'm no expert but my thoughts are that the temperature alone is damaging for the battery (and it will be ~warm since it is basically inside the laptop). Unless you have a way to change it the charge will also be at 100% which is also not ideal.
The margins of error are quite small considering that they sometimes explode well within their intended use case (which is not powered on 24/7).
The consequences of a fire in a battery is quite severe, and unlike normal laptop usage you probably won't be around it when it starts (or, worse, you might be asleep).
So, I'd err on the safe side and buy a UPS that at least covers the intended use case. For something as efficient as a laptop it isn't expensive either.
This is a great point. I'd likely have a tough time buying a laptop that didn't have a removable battery but sometimes with hand-me-down, I don't have a choice.
Usually, though, by the time they become my HTPCs, the batteries are completely shot already and so I recycle them at work.
form factor is a bit annoying, I do this with an old thinkpad and I'm thinking about finding one with a broken LCD to remove the screen assembly altogether and put the base onto a book shelf.
