Watch as NASA astronauts conduct 3rd spacewalk in 3 weeks

NASA astronauts Chris Cassidy and Robert Behnken completed a spacewalk Thursday outside of the International Space Station to replace lithium ion batteries for one of the station's power channels — their third spacewalk in as many weeks.

Running more than an hour ahead of schedule, they managed to complete the battery swaps in a single spacewalk rather than two. Their fourth spacewalk next week will now focus on other chores.

“Great job,” Mission Control radioed.

Watch NASA's video of the spacewalk on Twitter here:

Both astronauts are veteran spacewalkers. This was the ninth venture outside for both Cassidy and Behnken, according to NASA.

They swiftly removed six of the remaining old nickel-hydrogen batteries and plugged in three new lithium-ion units. The lithium-ion batteries — big, boxy units with a mass of more than 400 pounds (180 kilograms ) — are so powerful that only half as many are needed. The batteries store power gathered by the station's solar panels for use on the nighttime side of Earth.

Behnken, along with NASA astronaut Doug Hurley, launched from the United States and joined Cassidy on the space station on May 31. They were aboard SpaceX's Crew Dragon during the Demo-2 mission.

These spacewalks are the culmination of a series of power upgrades that began in January 2017 to replace nickel-hydrogen batteries with new lithium ion batteries.

During Cassidy and Behnken's spacewalk on July 1, the astronauts worked on tasks scheduled for later spacewalks, routed power and ethernet cables and laid the groundwork for future power system upgrades. Watch video from that spacewalk here:

These cables will provide better views on future spacewalks, according to NASA.

The upcoming spacewalk on July 21 will be the 300th spacewalk for U.S. astronauts. The first occurred when NASA astronaut Ed White left the Gemini 4 capsule on June 3, 1965.

The battery replacements, which will have a 20-year lifetime, will put the station in a much better configuration for the long term, said Kenneth Todd, deputy International Space Station program manager, during a recent NASA press conference.

Behnken recently discussed the spacewalk, and why it's important to replace the batteries, during a call to the space station from CNN Innovation and Space Reporter Rachel Crane.

"When the space station is in the sun, it's collecting energy and it needs to store for when it's in the dark," he said. "And so those batteries, as they're cycled time and time again, they wear down and need to be replaced. And so periodically that maintenance is required."