Apple has issued updates for MacBook, MacBook Pro, and MacBook Air notebook models to fix a rare battery issue. The updates are available via Apple's software updates page or through Software Update and the Mac App Store.
This update addresses a rare issue on some Apple notebooks where a battery that has accumulated more than 1000 charge cycles may unexpectedly shut down or stop functioning.
Update: MacRumors forum member Dempson looked inside the updates and found they are for the following machines:
MacBook7,1 (13-inch, Mid 2010)
MacBookAir3,1 (11-inch, Late 2010)
MacBookAir3,2 (13-inch, Late 2010)
MacBookAir4,1 (11-inch, Mid 2011)
MacBookAir4,2 (13-inch, Mid 2011)
MacBookPro7,1 (13-inch, Mid 2010)
MacBookPro8,1 (13-inch, Early 2011 or Late 2011)