New firmware update fixes battery problems on MacBook Air, MacBook Pro with Retina Display

Apple on Tuesday released new System Management Controller (SMC) updates for 2012-era MacBook Pros, 13-inch and 15-inch MacBook Pros with Retina Display, and MacBook Air mid-2012 and mid-2013 models. The updates are available through the Software Update system preference and through Apple's Support web site.

All SMC updates are listed as version 1.9, and all contain the same fix:

This update addresses rare issues where the battery unexpectedly stops functioning or the system hangs when the battery charge reaches less than one percent.

Source: 9to5Mac