Calibrating a MacBook battery

Li-ion batteries aren't exotic power sources these days: possibly, indeed, they're the most common type of battery used in consumer electronics. a Li-ion batteyr is powering your laptop (and a number of other devices) right now.

Li-ion batteries have considerably less memory effect than their predecessors and probably that's the reason why many of us don't worry that much about properly maintaining their batteries. In fact, Li-ion batteries performance degradation can be so slow that it is imperceptible for the user on a day-by-day basis, although this continuous process will typically reduce a Li-ion battery capacity by an approximate 20% per year. An consequence of this effect is a lack of accuracy on the battery charge meter some batteries provide, such as those that equip Apple notebooks.

Taking care of your battery

Ironically, Li-ion batteries do not require so big an effort to be used properly so that they can deliver their best performance to you. To say it plain: don't let electrons stagnate inside your battery and let them flow, instead. In fact, prolonged high charge periods reduce your battery life. High temperatures damage it as well. Therefore you should not be running your devices with the charger constantly plugged in, although it's a common practice for laptop users.

Ideally, you should let your battery discharge for time to time: that's why many laptop producers publish guidelines about battery usage patterns and calibration procedures. As stated, Li-ion batteries are subject to a process of reduction of their full charge capacity and, because of this process, your battery charge meter might start to lose accuracy: for example, it might display less than 100% when the battery if fully charged.

To reduce your battery wear and tear and to improve the accuracy of your battery charge meter, you should follow the instructions of your equipment to periodically calibrate the batteries of your appliances. In the case of a MacBook, as well as for most of its laptops, Apple has published calibrations instructions.

Calibrating your MacBook battery

These are the steps outlined by Apple to calibrate a MacBook Li-ion battery:

• Plug in the power adapter and fully charge your PowerBook's battery until the light ring or LED on the power adapter plug changes to green and the onscreen meter in the menu bar indicates that the battery is fully charged.
• Allow the battery to rest in the fully charged state for at least two hours. You may use your computer during this time as long as the adapter is plugged in.
• Disconnect the power adapter while the computer still on and start running the computer off battery power. You may use your computer during this time. When your battery gets low, the low battery warning dialog appears on the screen.
• At this point, save your work. Continue to use your computer; when the battery gets very low, the computer will automatically go to sleep.
• Turn off the computer or allow it to sleep for five hours or more.
• Connect the power adapter and leave it connected until the battery is fully charged again.

That's it. Remember to calibrate your battery from time to time depending on your usage pattern. If you use your laptop plugged in most of the time, calibrate it at least once a month.

What happens when my laptop "automatically goes to sleep"?

This may sound scaring to some of us but there's nothing to worry about. Almost every Apple laptop nowadays implement a "safe sleep" mode which if functionally very similar to Windows hibernation of Solaris' suspend and resume. Your work won't be lost because your machine state has been persisted to disk when your computer went into sleep mode. Even if your battery depletes completely (even if you replace it!), you won't lose any data and your laptop, when woken up, will restore its state from disk.