We have a whole house generator that runs on natural gas. When we first built our retirement home power outages were a somewhat common event, and with a well and septic system we decided that the cost was justifiable.

All of our communication (internet, phone, TV) comes & goes via satellite dishes. In the middle of a big rain/snow storm there is no communication. We have to find out if a landline phone service is even available here.

Here in northest Wisconsin even weather radio reception is marginal. Sometimes we'll get alerts, but most of the time we don't.

Oddly enough the state passed one of the largest legislative bills ever to provide broadband access to rural areas. A wireless broadband tower was built less than a mile north of us, but the trees completely block access, and I have no interest in building or maintaining a 100+ foot tall tower.

Even Elon Musk's system won't work here given the tree canopy. I've been told it'll work if we put the antenna on the peak of the roof, but I won't go on our roof to maintain it, so that's a no go.

That makes me wonder then; what UPS have you tried that won't run Michael2? Any I have will run unloaded even without issues and once you subtract the internal inverter load the runtime/power drawn is a pretty linear curve.

None! The whole point is that buying one and finding out after the fact that it doesn't work is a crummy plan. I'd like to know what the facts are instead of doing trial and error purchasing.

It's not a fiction that SOME UPS models and portable power stations shut down under low load. This is noted in the links I gave previously. Sometimes this "no-load shutdown" feature can be disabled, e.g., https://www.se.com/in/en/faqs/FA280865/ and sometimes it can't.

Sometimes people faced with this problem (having already shelled out money for a UPS) resort to electronic hacks to solve the problem.

To make things more confusing, sometimes the manufacturer (APC) says specifically that the UPS will shut down under low load, but users say it doesn't happen, and others say it happened to them. Need I mention that random sites on the internet do not always provide 100% reliable information? That's why I asked here, because I think it might be a bit more trustworthy.

And that's why I am interested in people's personal experiences with particular named UPS models that they personally have verified will run a 5W load. I did that with the big expensive and heavy one I have for my computer, as I mentioned above. But I'm looking for a cheaper solution that can be permanently installed next to my VoIP box.

I have two APC and one other brand that I've ran with no load to test them, so I haven't run across any issues personally with home/consumer models.
I could see the really big ones being like that.

But what power does your VIOP modem take, 5v, 12v, 19v?

Found a solution that met my specs:

APC CP12142LI Network UPS 12Vdc.

APC is a well-known reputable brand, this unit is specifically designed for 12v network devices (so it avoids the inefficiency of converting a DC battery voltage up to 120 VAC and then back down to 12 VDC) and it will keep my fiber terminal going for well over 24 hours. List price is $130; I got it for about $5 less (with free shipping).

I also bought a separate power supply for it (about $20) and an adapter cable to fit the terminal (about $7).

I had spotted this UPS a while ago, but it was out of stock all spring - supply chain issues I presume. I finally got it and installed it a few days ago. So far so good.

I've never seen that specific unit face to face, but APC is an excellent brand and they stand behind their stuff. I've sold and deployed quite a bit of APC gear in previous jobs.