I think a maxijet 1200 is something like 24 watts. Yes, Tunze Streams use less than that. So do the Turbelle's.

I had a large (850 va?) UPS for years. I ran a return pump on it for 3 or 4 hours no problem. You could probably run a Stream or Turbelle for quite a while. The battery backups are designed to run computer systems for up to half an hour. A computer power supply can be 300 to 500 watts and a computer monitor can be about the same. So you can see where a good size battery backup unit could run a 20 watt pump for hours.... For days though I'd think you'd want a generator.