I have a UPS and I also need a backup 12v battery setup for a spare emergency rig. Typically I would have to plug a 12v power supply into the UPS 120v which would lose a lot of energy. What about removing the inverter portion and tap straight off the battery?
Your typical consumer grade UPS is only designed to keep your computer (or whatever) running long enough to give you time to save your work and shut down the computer, as well as cushion equipment against power line transients.
As others have noted, the battery in a UPS is typically too small to power your rig for any real length of time, plus you could screw up the UPS by tapping off the battery. Plugging a power supply into the UPS is also inadequate, not only because the UPS won't power it very long, but since you're converting AC to DC and back to AC again, it's amazingly inefficient.
Best bet... get a power supply and gel-cell battery suitable for your current requirements, and connect them to the rig through a gadget like the Flint Hills Radio Low-Loss PWRGate, West Mountain Radio Super PWRGate, or Astron BB30M. The power supply will power the rig and at the same time float charge the battery; if the mains power goes away, the rig will instantly switch to battery.
I've used a setup like this on my home station for years with a 33Ah battery and a Low-Loss PWRGate, and it works like a champ.
