Hi, S. I can't help you much with info on battery powered back-ups, but as a result of a very misspent youth, I know a little about syphons. Remember that you have to keep the inlet higher than the outlet and you have to keep water over the inlet or it will break the syphon. They way my basement, the sump and the drain are arranged, there is not much height in the sump that is above the level of the drain. If yours is about the same, this might not work as well as you expect. There are water powered syphons that work about the same way as a steam locomotive water injector. This might be a better bet to investigate.