Updated 8:50 p.m. Eastern with updated spacewalk time.

LOUISVILLE, Colo. — NASA will postpone the remainder of an ongoing series of spacewalks at the International Space Station to upgrade batteries for its power system after a related component malfunctioned and needs to be replaced.

NASA announced Oct. 15 that the third in a series of battery replacement spacewalks that had been scheduled for Oct. 16, featuring NASA astronauts Jessica Meir and Andrew Morgan, had been postponed after a device called a battery charge/discharge unit, or BCDU, failed on the station over the weekend. The device is used to charge the batteries as part of the station’s power supply.

Instead, NASA will carry out a spacewalk Oct. 18 to replace the failed BCDU unit with a spare on the station. Meir and Christina Koch will perform that spacewalk. The two had been scheduled to perform an Oct. 21 spacewalk to replace batteries, the first all-female NASA spacewalk.

During a media teleconference Oct. 15, Megan McArthur, deputy chief of the NASA astronaut office, said NASA decided to have Koch and Meir conduct the spacewalk to balance workloads for the crew, given the number of upcoming spacewalks projected to take place in the coming weeks. “With the content of the EVA and balancing of the overall workload, it made sense for us to make the crew for this spacewalk this week Christina Koch and Jessica Meir,” she said.

In addition to replacing the BCDU, Koch and Meir will perform two other tasks outside the station, said Kenny Todd, manager of ISS operations and integration. The two will move some multi-layer insulation around other battery charger units, and then install hardware on the Columbus module to support a future external experiment platform.

In an interview here during a media event for Sierra Nevada Corporation’s Dream Chaser cargo vehicle, Kirk Shireman, NASA ISS program manager, said the BCDU units were turned off before an Oct. 11 spacewalk to replace batteries, but otherwise not touched. Three such units were switched off for the spacewalk, and two turned back on normally afterwards. The third, though, failed to turn on.

“We believe the battery is fine,” he said, but without a working BCDU, that power channel now produces only two-thirds of its rated power. That led to the decision to carry out a spacewalk to replace the charging unit.

Shireman said that NASA doesn’t plan to immediately resume spacewalks to complete the battery replacement work, a task the agency expected to take five spacewalks. “We’re going to stand down, probably for a few weeks,” he said, to determine if the BCDU failure was caused by something done during the battery replacement process. “We don’t believe that’s the case, but we want to go take some time and look at all the data.”

Todd said there’s “some level of concern” because another BCDU failed earlier this year during another battery swap. That unit was in a location that allowed the station’s robotic arm to replace it, an option not available here since the failed unit is at the end of the station’s truss.

There are 24 BCDUs on the station, with three or four spares on the station and none on the ground. “There’s going to be a lot of emphasis in the near term on trying to understand what operationally we might be able to do to mitigate any concerns with installing these new batteries,” Todd said.

The timing of the remaining battery replacement spacewalks, including how many more will be needed, will also depend the ability to keep a mobile work platform by the site with equipment needed for the battery replacement. “There are some implications of leaving it out there” that are still being studied, Shireman said. NASA had planned to complete the spacewalks Oct. 25.

The battery replacement spacewalks were just the start of an intense period of activity outside the station. Later this fall Morgan and Luca Parmitano will carry out an additional set of five spacewalks to replace coolant pumps on the Alpha Magnetic Spectrometer (AMS) instrument on the station. That effort is complicated by the fact that the AMS was not designed for in-space repairs, requiring special training for the astronauts.

Besides the battery replacement and AMS repair spacewalks, Russian cosmonauts Alexander Skvortsov and Oleg Skripochka are scheduled to carry out a spacewalk Oct. 31 on the station’s Russian segment.