CAPE CANAVERAL, Fla. (AP) — A four-year effort to modernize the International Space Station’s power grid is finally complete. A pair of NASA astronauts installed the last battery during a spacewalk Monday, and the unit checked out well. It was the second spacewalk in five days for Mike Hopkins and Victor Glover. Over the weekend, flight controllers in Houston used the station’s big robot arm to replace the last batch of old batteries with a new, more powerful one. Hopkins and Glover quickly put the finishing touches on this newest lithium-ion battery. Their work completes a series of spacewalks that began in 2017.