I have a small Belkin UPS that's been retired, and I too have been planning to power it with my solar panels via an external 12V battery. This model lets you turn off the annoying beeper alarm, which is a bonus.

The internal connections are straightforward. I think I'll run a wire to a good earth ground for safety and static discharge.

I only plan to use it for fussy electronics that can't handle my modified sine wave inverters.