Anne McClain was due to join Christina Koch for the mission on Friday, but was forced to pull out due to a shortage of medium-sized suits.
Nick Hague replaced her and joined Koch in installing new and stronger batteries for the station’s solar power grid.
Its outdated nickel-hydrogen ones are being swapped out for lithium-ion ones, which store power collected by the solar wings and keep the outpost running when it’s on the night side of Earth.
Mr Hague and Ms Koch arrived at the space station two weeks ago.
A third spacewalk is planned for 8 April, but that will also be mixed gender.