Some Apple portable computers (PowerBook G4, iBook, MacBook Pro, MacBook, and MacBook Air) may not show the battery as 100 percent charged in Mac OS X, even when the power adapter is connected.
The battery may appear to stop charging between 93 percent and 99 percent.
This is normal. The batteries used in these computers are designed to avoid short discharge/charge cycles in order to prolong the overall life of the battery.
When setting the Mac OS X battery status menu bar icon to display charge state by percentage, you may notice that the reported charge stays between 93 or 95 percent and 99 percent.
To allow the adapter to recharge the battery to 100%, simply allow the charge to drop below 93%. The adapter will automatically recharge the battery to 100%.