Within three hours of floating outside, Garrett Reisman and Michael Good had plugged in the remaining two new batteries. Four were installed during Wednesday's spacewalk by Good and another spaceman.
"The batteries are done," one of the spacewalkers said. "Yeah!" shouted the other. "Can you believe it?"
Replacing the station's original 10-year-old batteries was harder than it sounded. There were many bolts to undo then redo and the batteries were bulky: 3-foot-wide boxes, 375 pounds apiece.
With shuttle flights ending this year and another decade of space station operation looming, NASA wanted the orbiting outpost to have all fresh batteries. Six batteries were replaced last summer. The nickel-hydrogen batteries are charged by the solar wings and provide electrical power to the space station during darkness.
Each one cost $3.6 million, or nearly $22 million for a pack of six.
The removed batteries were packed aboard a platform for Atlantis' trip home next week.
Besides the battery work, the astronauts hooked up a new a cable for the station's cooling system and tackled some other odd jobs. They stole a view of Italy as they soared more than 210 miles overhead.
"Fantastic," Reisman said. "Smell all the pizza from here."
Later, the astronauts could see the two shuttle launch pads and the landing strip at Florida's Kennedy Space Center.
"Houston, we've got the field in sight," shuttle pilot Dominic "Tony" Antonelli radioed from inside. "We'd rather you not land just yet," Mission Control replied.
The spacewalkers were so eager to get going Friday morning that they went out early. As the pressure slowly dropped in the air lock, Reisman commented: "It's like standing on your bathroom scale and waiting for the needle to go down."
Atlantis delivered the batteries last weekend along with a new Russian-made compartment. The chamber was opened Thursday, but had to be sealed again when metal filings were found floating inside. Mission Control said air scrubbers should clean up everything.
Atlantis will undock from the space station Sunday for the last time. Only two more shuttle missions are on the books, both of them scheduled for this fall and set aside for NASA's two other shuttles.
NASA and some members of Congress are pushing for one more flight of Atlantis, next June. The Obama administration would have to give its blessing.
President Barack Obama wants to end the shuttle program fairly soon so NASA has more money to spend on developing the technologies needed to send astronauts to asteroids and Mars. Russian rockets will continue to ferry U.S. astronauts to and from the space station until commercial companies can perform the job with their own spacecraft.
The space station is expected to keep operating until 2020.