Like virtually all mobile computer manufacturers, Apple recommends that users calibrate their laptop batteries every few months, as Scott pointed out a couple of years ago. Unlike many manufacturers, however, Apple does not include a utility to automatically perform a calibration. Given Apple's uncanny ability to make things user-friendly, this seems like a bit of a glaring oversight.
What are the benefits of calibration? Primarily the goal is to ensure that the microprocessor in your battery provides an accurate estimate of how much time you have left on the battery. Over time it can lose track of just how much juice your battery has in it, and calibration gives it a very accurate reading on the battery's health.
Older battery technologies also benefited from a process called conditioning, which was typically performed the same way as a current battery's calibration process. In a nutshell, you fully charge the battery, fully discharge it, then fully charge it again. It's unclear whether modern lithium batteries gain anything in an actual capacity perspective from this process, or if it is simply a calibration of the microprocessor for the purpose of providing accurate time estimates.
Now, if it seems that accurate time estimates are not all that important, consider that you could actually be losing battery time because your laptop is shutting down prematurely. In other words, there might actually be extra juice in your battery that you're not able to use because your laptop thinks the battery is almost depleted when it's not.
So if you'd like to perform a calibration manually on your modern Mac portable*, follow these steps taken from Apple's battery calibration knowledge base article:
- 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 with 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, you will see the low battery warning dialog on the screen.
- Continue to keep your computer on until it goes to sleep. Save all your work and close all applications when the battery gets very low, before the computer goes 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.
If you have an older Mac portable like an iBook or PowerBook G4 other than the PowerBook G4 (15-inch Double-Layer SD), you can skip steps 2, 4, and 5 in the calibration process.
As you can see, while not complicated, battery calibration is a fairly involved process. A utility that walks the user through the process would certainly be useful, and would likely result in a lot more Mac users taking care of their batteries. If you're interested in a tool to check up on the health of your battery, check out TUAW favorite coconutBattery or the venerable iBatt.
* With respect to these instructions, "modern Mac portables" refers to the following: PowerBook G4 (15-inch Double-Layer SD), MacBook (all models), MacBook Pro (all models), and MacBook Pro (17-inch) (all models)