How do you change a battery in zero gravity? Step by careful step.

January 6, 2017 --Two astronauts went spacewalking on Friday as they began the two- to three-year task of replacing all the batteries for the International Space Station's power grid. NASA astronauts Shane Kimbrough and Peggy Whitson, the world's oldest most experienced spacewoman, undertook a risky 6.5-hour spacewalk outside the 250-mile-high station. Their mission was to wire up three new lithium-ion batteries, each about the size of half of a refrigerator that Houston controllers had already replaced remotely, via the station's onboard, 11-foot-long-armed robot Dextre. The project to swap out the station's decade-old nickel-hydrogen batteries began on New Year's Eve, 2016. The lithium-ion replacements are much more efficient, meaning only 24 will be required to replace the 48 old ones.