I personally just a regular PC desktop because I need the expansion slots. But SFF PCs are amazing home servers, and have more than enough power for what you actually need.
Also don't forget laptops. They're designed from the group up to be efficient AND have a built in UPS. My home server for the longest time was an old laptop with 32 gigs of ram (back when that was a huge amount).
So I bought a 2018 Dell laptop with a messed-up screen. Now when there is downtime, the laptop stays on, connectivity goes away for a few mins (which doesn't bother me) and everything is resolved fast.
So, I suggest either your desktop+UPS, or a 5yo laptop (just make sure it's 'high-end' - for its age). I then upgrade RAMs & SSD/M2 from Crucial (I like the convenience of their app) so I end up making decent "server laptops" for under €300.
- batteries might not like being constantly charged. You might kill them, hopefully they don't swell. It might be interesting to remove the battery if you can, but then you indeed lose the feature they provide to survive power cuts.
- the disk drives are constantly parking their heads, make sure that the parking policy is ok (won't wear them to fast). Maybe less of an issue with many laptops coming with SSDs.
- some laptops just heat too much and power off too often, especially in summer.
- their hardware might end up dying quite fast.
I think I would still use an old laptop as a home server if I had suitable one, especially since it helps making such a machine useful for a longer time even when they are not quite usable for the web of today anymore (I like the reuse spirit it has), but I've found my rockpro64 (a nice single board computer) way more reliable in this role.
I guess YMMV depending on the laptop models. I can definitely imagine that a solid laptop with its battery removed can work well as a server.
I've never had any laptop die while operating like this. I only replace them when I replace my primary use laptop with something new, demoting my last primary use laptop to the server role.
I’m surprised that the Linux distributions I use don’t do this automatically but I bet it could be configured.
If I'm to believe this bug report [1], KDE actually offers throttling charge, but I suspect the Linux kernel lacks support for this kind of stuff for many laptops, maybe also because sometimes the laptop itself does not support this.
Apparently, one should be able to see these files on a supported laptop:
/sys/class/power_supply/BAT0/charge_control_start_threshold
/sys/class/power_supply/BAT0/charge_start_threshold
/sys/class/power_supply/BAT0/charge_stop_threshold
But thanks for reminding me this. I was considering using an original PinePhone as a Bluetooth receiver. Unfortunately, Wifi and Bluetooth require a battery to be present in this phone and I was a bit concerned leaving it plugged in at all times. I'll need to check if the kernel the hardware and support this. Still a bit concerned that the battery will be wearing out fast, I'm afraid Bluetooth will be using the battery power even if the phone is plugged, which is a bummer.
Would be interesting to know which chipsets support it.
Does a computer with charging throttle like described draw power from battery too, or does it use the power from the plug directly?
A battery level check every five minutes should be more than enough, not a big draw from the battery for a laptop.
Frame.work laptops have a firmware setting to stop charging at 90%, to extend battery life.