Two NASA astronauts on the first of two spacewalks outside the International Space Station made swift work to help with the replacement of old batteries with new lithium-ion units. They even had enough time left over to perform several get-ahead tasks.

Extravehicular Activity 38 began at 7:23 a.m. EST (12:23 GMT) Jan. 6, 2017. It was performed by NASA astronauts Shane Kimbrough and Peggy Whitson. The goal was to install three adapter plates next to three lithium-ion batteries that were installed robotically late last week.

On Friday, NASA astronauts Shane Kimbrough and Peggy Whitson will venture outside the 400-metric-ton International Space Station on the first of two spacewalks to begin a multi-year process of upgrading the outpost’s power system.

The spacewalk, Extravehicular Activity 38, will see the two Expedition 50 astronauts install battery adapter plates and help with the swap-out of old nickel-hydrogen batteries with new lighter and more efficient lithium ion units.