Whenever my MacBook's battery is 99% full, it stays there and never become full charged (100%). This is normal. The batteries used in Macs are designed to avoid continuous charging or short cycle charging, i.e. the battery drops 1 or 2 % then charges back to 99%, which will shorten battery life. It is the best to let the battery run down to below 40% every now and then and then do a full recharge (between 95-99%).
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 95 percent and 99 percent. The adapter will not charge the battery to 100% automatically if it will add additional wear to the battery.
Therefore, if your battery status stays at 95-99% and not charging you can disconnect the charger.
