Two flight engineers with NASA completed the first spacewalk of this year on the International Space Station (ISS) on Friday to upgrade the space lab's power system.

Nick Hague and Anne McClain's spacewalk lasted six hours and 39 minutes and ended at 2:40 p.m. American Eastern Time, according to NASA.

The two astronauts replaced nickel-hydrogen batteries with three newer, more powerful lithium-ion batteries for the power channel on one pair of the station's solar arrays.

They installed adapter plates and then hooked up electrical connections on the starboard truss, NASA's live webstream showed.

The batteries were transported to the station in September 2018 aboard the Japanese H-II Transfer Vehicle.

The batteries store power generated by the station's solar arrays to provide power to the station when the station is not in the sunlight, as it orbits the Earth during orbital night, according to NASA.

They also worked to remove debris from outside of the station.

McClain and another female flight engineer Christina Koch are scheduled to venture outside next Friday to work on replacing the batteries on a different power channel. It will be the first female-only spacewalk in history.

Additional batteries will be replaced as part of this power upgrade over the next couple of years as new batteries are delivered to station, according to NASA.

(Top image: NASA astronauts Nick Hague (top) and Anne McClain work to swap batteries in the Port-4 truss structure during the spacewalk on March 22, 2019. /NASA Photo)