MacBook Air owners who haven't checked Software Update for a couple of days will now find a firmware update awaiting them there. The download adds support for the "latest service replacement batteries".

All Air lithioum-polymer batteries are so described because they can only be - officially - swapped out by Apple itself, the power packs being hardwired into the machines.

Since the orginal Air was released more than 17 months ago, in February 2008, the machine has been revamped twice, most recently last month.

Tweaks to the battery's on-board management electronics are inevitable, and it's to enable these with older Airs and to possibly pave the way for further battery revisions that Apple has posted the 623KB update. ®