The problem with that is a lot of people who need the back up sump pump are on a well and if the hydro is out, then.....
Rattletrap, Myers makes one too, not too sure about retail models, but we get ours from Wolseley, a plumbing wholesaler. They can move a lot of water. Not too many problems with them, just make sure you put the check valve for the main sump pump between the back up and the main, or you'll just be recirculating the water.