The 2009 battery has a lower capacity at 73 Wh vs the 2010 battery (A1321) at 77.5 Wh. The MacBook Pro 15' 2009-2010 batteries are electrically compatible. The MacBook Pro 13' Retina L2013-2014 batteries (A1493) are the same at 71.8 Wh. The MacBook Pro 13' Retina 2012-E2013 batteries (A1437) are the same at 74 Wh.
The MacBook Pro 13' unibody batteries are electrically compatible with all models. MacBook Air 13' unibody batteries are electrically compatible with all models. The 2010 battery (A1406) connector is physically in a different location and will not fit in the housing of the 2011-2015 battery (A1495). MacBook Air 11' batteries are electrically compatible with all models.
