Yeah, consumer UPSs tend to scale their inverter capacity along with their battery capacity, which means if you're shopping for huge capacity for long runtime, you end up paying extra for a huge inverter you don't need.
I've gone the other route, with a simple power supply that charges an ever-evolving fleet of whatever cheap 12-volt batteries aren't doing anything else, which then feeds DC-DC converters for the various loads. For stuff that's natively 12-volt like my wifi router and cable modem, I just run those directly off the battery rail.
This setup is quiet, efficient, and presently runs the modem, router, service pi, and my RIPE Atlas probe, for somewhere upwards of 20 hours, for something like $150. If I added a 12v-to-48v converter and a small PoE switch feeding a few cameras, it would probably cut the runtime in half, but I could just throw more battery at it for pennies on the watt-hour.
I've gone the other route, with a simple power supply that charges an ever-evolving fleet of whatever cheap 12-volt batteries aren't doing anything else, which then feeds DC-DC converters for the various loads. For stuff that's natively 12-volt like my wifi router and cable modem, I just run those directly off the battery rail.
This setup is quiet, efficient, and presently runs the modem, router, service pi, and my RIPE Atlas probe, for somewhere upwards of 20 hours, for something like $150. If I added a 12v-to-48v converter and a small PoE switch feeding a few cameras, it would probably cut the runtime in half, but I could just throw more battery at it for pennies on the watt-hour.