One of the things Apple seems to be very good at is managing battery "overcharge": my 5 years old MBP reports ~90% battery capacity but a relatively low amount of cycles (~200) because it's almost always tethered. Other companies seem to handle that less well and have the battery health fall much faster.

It it possible Apple overprovisions their batteries such that they only ever charge the physical calls up to an ideal level (~80% or whatever, of nominal Wh capacity), and then they show in software a 100% charge? If the battery is larger than it needs to be, the extra headroom would allow long usage on a "full" charge while preserving cell longevity. In time when capacity does diminish, software could also raise the full-charge point from ~80% of physical capacity closer to the nominal physical cell capacity.

This would be similar to what SSD manufacturers do with drive sizes. There are more memory cells on the die than the sticker capacity, and as cells fall out of use (due to failure or maximum number of write cycles) extra cells are rotated into use to maintain speed and capacity.

Here's a link to my MBA performance: http://imgur.com/2UVFmIU

Bought Nov 2013, now has over 250 charge cycles and is still at 90% of original capacity.

How would I generate this graph for my MBA?