Apple released its MacBook Air SMC Firmware Update 1.2 patch yesterday, a 623 kilobyte download that offers the following fixes and changes per the web site:
“This SMC firmware update adds compatibility for the latest service replacement batteries…. After this update has successfully completed, your SMC Version will be: 1.23f20 [for original MacBook Air models, or] 1.34f8 [for more recent models].”
SMC Firmware Updates generally control the System Management Controller on Intel-based Macs. The SMC controls power and thermal management features, including the battery and fans. In this case, new replacement batteries from Apple are apparently different enough that they require the use of this updated version of the SMC firmware.
The update can be downloaded directly or snagged and installed via Mac OS X’s Software Update feature and requires Mac OS X 10.5 or later to install and run.