what are you trying to back up? The one from the ebay link has a constant rating of 3300 watts which isn't that much. You might consider looking around craigslist. I bought a 7500 watt unit for $550 and it was only 6 months old. Also look for the ones with a larger muffler on them because they will make less noise. said:
This unit will run everything in my house but the clothes dryer, and the water heater, just not all at once.
I can run the gas furnace, and the aquarium stuff minus the T5s at one time.
I can run the fridge, and freezer, and aquarium stuff minus T5s at the same time.
I can run 2 window units, and the aquarium stuff minus T5s at one time.
Am I missing something?