Not only can you run only one (at least on the Honda), but the 20 amp outlets on the stopped generator still work. I first realized it would work when I ran one out of gas (before I built my auxiliary fuel tank) and everything worked fine on one generator (no AC on).
Not sure on the Champion, but with the Honda you can turn ECO on and off anytime. Even with the AC on, I never run on the ECO setting and my "twins" start the 15K AC.
By the way Professor, I can run the AC with one generator (after it has started) if the batteries are pretty well charged and there are no other draws, but the poor little thing screams. I just don't have the heart to do it. It would probably go to overload in a short time anyway.
