Why over complicate it with electronics? It’s a computer.

Just have your device shutdown when it can no longer poll another device. For example, if the router or some other network device isn’t contactable for longer than two minutes, it might indicate that the power is out.

The router is one of the first things I put on a UPS. The telco equipment likely has fallback power as well.

Sure, you could find some device that isn't on a battery backup and ping it regularly. But this approach forces the device on your UPS to shutdown as soon as power is lost. That buys you a clean shutdown, but you don't get the added benefit of being able to run without interruption during a brief brownout.

> Just have your device shutdown when it can no longer poll another device.

Most people want their devices to stay up and running on battery as long as they can, not just shut-down immediately after utility power goes down. Without somehow measuring the battery voltage, you can't estimate how much run-time your devices have to work with.

And couple of months later you are investigating why the branch gone dark in the middle of the day.

No.

Devices should survive powerloss, devices can have a graceful shutdown from an external source.

Key is in your "might".

If you’re proposing to support a whole branch without a proper UPS, then your employer needs to reevaluate their hiring choruses.

It's more common for the employer to cheap out and not to buy UPS than for a sysadmin to propose a lack of UPS.

In your example even simply updating router OS/FW would case the router to reboot and your script will gladly shutdown the server.

I heard of connecting an old modem to a serial port for this purpose. If it doesn't respond to any AT commands then power may be out.

Any networked device will do - switch, router, etc. If there's no link on the port, power is down. USB-C Ethernet adapters with power pass-through will generally power the Ethernet module off the USB-C power port even if no host device is plugged in. USB-to-Ethernet adapters may also light up the port even if only connected to power (and not a host device).

And you call that "simple"?

Much simpler than sourcing and jury rigging some components into a usb interface. You’d need to set up some scripting for that anyway.

You could do it with a bash one liner

...while also keep a number of network devices always connected, reachable and correctly configured.

Have one router break or someone disconnect one cable and your servers will power down.

"simple".

That's not hard to do, for some networked devices that step amounts to just plugging it into a power source and connecting it to the network. I haven't had to touch the configuration of my wifi printer for example since I plugged it in to the wall years ago.

Sure but you'd need bigger pockets, probably even a bigger backpack.

Also a much bigger timeframe for testing and development. This isn't something you slap together in a weekend and call good. More like building an experimental drone than putting together a 3d printer kit or building a PC

No idea what you're talking about here. Solar charge controllers are quite mature and do exactly what is needed. You're literally putting a few wires on the right terminals, and a few connectors.

Only the low-battery signal would require a bit of work, but that is option and isn't found on ANY devices available off-the-shelf so it's not possible to buy your way around that.

Sure the "DC UPS" are basically "simple dumb batteries", but the sort of loads that you'd probably run off them and the expected runtime of each tends to be quite different.

Guessing the average AC UPS that someone might back a desktop with might last 5 minutes (or in a data centre long enough for the generators to kick in). A "DC UPS" running a router or a raspberry pi likely has a runtime measured in hours. Still would be nice to have monitoring info available, but more time for human intervention to shut down if need be.

"you might as well roll your own for less cost and much more runtime..."

Depends on how much gear you want to power. If you just want to keep a raspberry pi online a few hours I doubt you'd save much money (if any) rolling your own. Could be fun as a project though.

I got a large power bank (Bluetti EB55) to get me through the expected power cuts this winter. Supports charging from mains or solar while supplying power. Of course at £900 it's hardly a cheap option ...

If Europe has rolling blackouts this winter, the purpose is to reduce energy, and hence gas, consumption.

If everyone were to charge a battery bank when the power is on, to see them through the time when it is off, the net result would be increased energy consumption, due to efficiency losses.

That would only be true if people are charging huge batteries that sustain their full home energy usage. If they're only charging small batteries to sustain the most important devices in their homes, the usage will still be much lower.

Additionally, peak/off-peak is a thing. The grid may have excess power from wind and solar when conditions are idea. Charging your batteries during those times will not have any negative effects.