The problem to be solved was: during a power outage, I no longer wanted to lose my landline phone and WiFi.

A previous router I had required 2A, while the newer one I have now draws 2.5A (these are indicated on the device labels). I couldn't find another mini UPS that provides certified output of 3A at 12VDC!

Installation: simply place the UPS device between the power supply that plugs into the socket (230VAC / 12VDC) and the router: it has an input for a DC 5.5mm/2.5mm plug (like the power supply) and an output with a cable and the same plug. Super easy. (In case the power supply and the supported device have different pin sizes on the plug, the package also includes adapters to change from 2.5mm to 2.1mm or 1.7mm plugs, male and female. I didn't need them, though...).

Before installation, it requires a full charge on its own, the LEDs on the front show the charging progress.

Advantages:
- Brand name manufacturer (APC).
- Clear specifications (see photo).
- Very compact device.
- Very easy installation.
- 2500 mAh lithium-ion battery.
- It makes no noise.
- It does not heat up, does not emit heat.
- Powered by 12VDC, outputs 12VDC, no losses.
- The LEDs provide all possible information about the UPS status (see photo).

Disadvantages:
- To power a second device, it requires a workaround (*).
- It is expensive: it costs as much as the cheap UPS (230/230VAC), which on one hand have many sockets, but on the other hand are bulkier, have lead batteries (which require more frequent replacement), and have thermal losses.

One can weigh the pros and cons. I ended up with the small/compact/expensive/12V UPS.

(*) If you have, as I did, a Nokia converter from fiber optic to copper, then you need to supply 0.5A for that consumption as well, to keep your router alive during a power outage. Since the UPS only has one plug, you need a "Y" (a splitter) to share between the two devices. Well, don't search, there is no ready-made "Y" for DC plugs of 5.5mm/2.5mm (outer/inner diameter). You have to make it yourself (with a soldering iron). But even so, it's worth it because the UPS provides up to 3A at the output, which is sufficient for both devices!

Finally, a request to APC:
- Please, dear ones, include a "Y" with two DC outputs, even as an additional extension on the cable! So that someone can easily connect not only the router but also the fiber optic to copper converter...