How to Calibrate Your MacBook, MacBook Pro, or MacBook Air Battery
1.Start by ensuring your Mac is fully charged. Don't go by the battery menu item; instead, plug in the power adapter and charge your Mac until the light ring at the charging jack or the power adapter's light turn green, and the onscreen battery menu indicates a full charge.
2.Once the battery is fully charged, continue to run your Mac from the AC adapter for two hours. You can use your Mac during this time; just be sure the power adapter is plugged in and you're running off AC power and not Mac's battery.
3.After two hours, unplug the AC power adapter from your Mac. Don't turn your Mac off; it will transition to battery power without any trouble. Continue to run the Mac from the battery until the onscreen low battery warning dialog appears. While you wait for the low battery warning, you can continue to use your Mac.
4.Once you see the onscreen low battery warning, save any work in progress, then continue to use your Mac until it automatically goes to sleep because of very low battery power. Don't perform any critical work after you see the low battery warning because the Mac will go to sleep before long and with no other warning. Once your Mac goes to sleep, turn it off.
5.After waiting a minimum of 5 hours (longer is fine, but no less than 5 hours), connect the power adapter and fully charge your Mac. Your battery is now fully calibrated, and the internal battery processor will deliver accurate battery time remaining estimates.