Apple has released a set of EFI firmware updates to address a rare problem where some systems might unexpectedly shut down or stop functioning after the battery has been used extensively.
Apple's determines battery health in part by the number of charge cycles it has been through (one charge cycle being a sum of partial charges that equates to one full charge), and depending on the system claims that batteries should last between 300 and 1,000 charge cycles. However, a rare problem in some systems might result in a nonfunctional computer if the system detects that 1,000 charge cycles have been surpassed.
To fix this problem, Apple has released three EFI firmware updates for the MacBook Pro, MacBook Air, and MacBook. The updates are small patches and should be available by going to the Software Update section in the Apple menu, but can also be downloaded and applied manually from the following links (the updates can only be installed on systems for which they are intended):
Being firmware updates, be sure you have the systems attached to a reliable power source and do not disturb the update process. The system should show a small progress bar during the update and should restart at least once during the installation. As always, be sure to fully back up your system before apply these updates.