For that you nee to do a battery calibration. This can be done on existing battery on my iBook, PowerBook, MacBook, MacBook Air, and MacBook Pro.
MacBook battery has an internal microprocessor that is able to estimate the amount of power in a good battery while charging or not. Calibration of the battery needs to be done regularly to maintain the accuracy of estimates of battery on the MacBook screen. Battery calibration should be performed when the MacBook first time will be used.
Afterwards, you can perform on a regular basis every few months.
If you're accustomed to using the MacBook uses a power source directly and rarely turn on the MacBook using battery, the battery calibration should be performed once a month. For all versions of MacBook and MacBook Pro you can perform the following steps:
Install the adapter and do the charging on the MacBook until the battery until the LED is green and the battery meter on the screen indicates the battery is fully charged.
Allow the battery to rest about 2 hours, remained in a state of charging. You can use the MacBook in 2 hours during the adapter remains connected to the mains.
3. Remove the adapter from the power source without turning off the MacBook. Use a MacBook until the warning appears on the screen that says the battery in a state of low.
4. Save all your work. Continue working until the battery is low and the MacBook switches off (sleep).
Turn off the MacBook or leave in a state of sleep to five hours or more. After five hours or more pairs of longer battery adapter and leave it filled to the brim.
When the MacBook battery mode automatically changes to 'sleep'. In this position the battery is actually still have little power, but need to rest for a while. If the battery is completely empty then the MacBook would be forced to shut down.