The key were the crystals, the ones found in the black rocks in the ejection zone. They were batteries.
Hutch who figured out how to install them safely in the alien machines. It did not take long for New Deaver City to come alive with rolling heptahedrons, floating spheres and giant undulating robot worms.
The Ring builders had stocked the city with millions of the devices and the crystals were plentiful Earthside. No one had to fight over access; right of way was a different story.
Mayor Monica worried aloud, “I don’t think these things were left here for us.”