New or old, all of the MacBook, MacBook Pro, and MacBook Air portables use a battery that has an internal processor designed to maximize battery performance. One of the functions of the battery's internal processor is to estimate remaining battery life by analyzing the current state of the battery charge, as well as the rate at which power is being consumed.
In order to make accurate predictions about remaining battery charge, the battery and its processor need to undergo a calibration routine. The calibration routine helps the processor gauge the battery's current performance and make accurate predictions about the remaining battery charge.
When to Calibrate Your Battery
When you buy a MacBook, MacBook Pro, or MacBook Air, you should run the battery calibration routine during the Mac's first day of use. Of course, many of us end up enjoying our new Macs so much we forget all about this necessary step. Luckily, it doesn't hurt the battery if you forget to perform the calibration routine; it just means you're not getting the best possible performance from the battery.
Once the battery has been calibrated, its remaining time indicator will be much more accurate. However, over time, as the battery accumulates charges and discharges, its performance will change, so you should perform the battery calibration routine at regular intervals. Apple suggests calibrating the battery every few months, but I've found that the appropriate time between calibrations is highly dependent on how, and how often, you use your Mac. With that in mind, it's a safe bet that calibrating your battery as many as four times a year won't be excessive.
How to Calibrate Your MacBook, MacBook Pro, or MacBook Air Battery
- 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.
- 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 the Mac's battery.
- 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.
- 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.
- 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.