I don't know if you're just wanting a non stop motion device, or an endless supply of energy. If i remember right they have already done both. There's a rather eccentric fello (nick named peterpan of all things) who has re-discovered the original battery. It's a crystaline battery cell that picks up latent energy and converts it into an electrical charge. In theory, it doesn't run out of power since it neither stores nor makes it, it's merely a conduit for what's already there.