The Mars expedition Rover B, dubbed Opportunity, has been delayed since 24 June by a series of mishaps ranging from bad weather, to warped insulation to an errant fishing boat that wandered into restricted waterways just before lift-off.
The new launch target is now scheduled for Monday 10:35 (02:35 GMT).
“The battery must be removed and replaced,” said NASA spokesman George Diller.
NASA has until 15 July to launch the $400 million mission before earth and Mars move out of alignment, although NASA said it was studying alternate routes on the 480-million km voyage that might extend that launch window by as much as two days.
If NASA cannot make the window, the Delta 2 rocket will have to be disassembled and the spacecraft returned to its clean room until November 2004.
Opportunity’s twin, Spirit, is already speeding toward the red planet following a 10 June lift-off.
The six-wheeled robotic Rovers are set to arrive at Mars in January.
They will roll across the desolate martian landscape for about three months, taking photographs, drilling into rocks and scooping up soil samples.
Their job is to determine whether large bodies of water that existed on Mars more than a billion years ago lasted long enough for life to evolve. Future missions will search for evidence of that life.
Weather officials have forecast a 70 percent chance of acceptable weather for launch on Monday.