Q I could not resist buying a MacBook Air, and have ended up with yet another MagSafe mains adaptor. In a quest to rationalise and simplify hardware, could I power my new Air using a MacBook Pro 85 W MagSafe adaptor?
A There are three interlinked issues in trying to do this.
First, the mains adaptor needs to deliver sufficient power for the Air. As the latter should only draw 45 Watts, this should not be an issue if you use an 85 W adaptor.
Second, the MagSafe adaptor has to fit the port on your Air. Some older MacBook Pro adaptors are a slightly different size and shape, and will definitely not work: if both adaptors are MagSafe 2 or can use an Apple converter, you should be fine.
Third, the charging software in your Air needs to recognise the MagSafe adaptor being used and work properly with it. It is this last issue that was the great unknown, until Apple published this helpful guide which makes it clear that an 85 W MagSafe 2 adaptor should be fine for both your MacBook Pro and your Air.
Updated from the original, which was first published in MacUser volume 27 issue 3, 2011.