The batteries used in earlier Apple portables were nickel-cadmium (NiCad) or nickel-metal-hydride (NiMH) varieties. To remain in optimal condition, these batteries required complete discharge-charge cycles, that is, the batteries needed to be run down to zero and then fully recharged afterwards. Failure to do this promoted the development of crystals inside the power cells that reduced the overall power capacity of the battery. This loss of charge capacity became known as the "memory effect".
Li-Ion batteries don’t suffer from this problem, allowing the user a much freer hand when it comes to discharging and recharging the battery inside a MacBook or MacBook Pro. Still, there are some ways to maximize the number of useful charging cycles. First, avoid completely draining the power down to zero. Instead, replace the battery once the battery drops to less than 20% its normal charge with another battery, or else plug the computer into an outlet. Second, try not to drain the battery too rapidly. Frequent activities that rapidly use up battery charge, such as playing DVDs, will end up shortening the useful life of your battery.
But the single most important thing you can do with the Li-Ion battery inside your notebook computer is to discharge the battery occasionally as a maintenance step, especially if your notebook computer operates mostly from the outlet supply or spends long periods of time in storage. Apple recommends completely discharging the battery once a month. It’s worth adding a monthly reminder to your calendar so that you perform this essential maintenance routine on a regular basis.
Besides keeping the battery in tip-top condition, periodically discharging the battery in your notebook recalibrates its built-in power management software. The power management software requires a full discharge-charge cycle to "learn" how much energy the battery can store and to provide useful estimates of battery life. If this software isn’t recalibrated periodically, such estimates become increasingly unreliable, particularly as the battery itself ages and stores less charge than when the power management software was initially calibrated at the factory.
Figure 2 Add a recurring monthly event to your calendar software as a reminder to completely discharge and recharge your MacBook or MacBook Pro. This action will extend the useful life of the battery.