Even the International Space Station needs its batteries changed every once in a while. This past Friday, NASA astronauts Shane Kimbrough and Peggy Whitson took on the task, beginning the swapping-out process during a six-hour spacewalk.

The current batteries, nickel-hydrogen units that recharge in the sunlight, have been powering the ISS for 18 years. This year, they’ll be replaced by a lithium-ion design, which have a better storage capacity and are essentially just enormous versions of cell phone batteries, Whitson told NASA TV.

The swap is a two-trip effort—the actual batteries will be plugged in this Friday, Space.com reports. This time, Kimbrough and Whitson installed adapter plates and electrical connections. In the process, Whitson tied the record for most spacewalks by a female astronaut—seven.

Next time you balk at getting on the ladder to replace your smoke alarm batteries, take a deep breath and think of these two.

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