Each battery unit contains a monitoring processor which operates automatically and standalone—without any interaction by the computer. It observes the battery and tries to operate it at such conditions that lifetime is extended as long as possible. For this reason, regular care and maintenance is not necessary for up-to-date batteries. The battery can neither be overcharged, nor deeply discharged, because the processor prevents this. Nevertheless, you should consider the following handling rules on which the battery processor can have no influence:
AVOID TOO HIGH AND TOO LOW TEMPERATURES. You should not leave the battery or the mobile computer in a car. Don’t keep your computer switched on (i.e. not in sleep mode, but in “clamshell operation”) when it is in a bag or on a soft underground which might cover the venting openings.
DON’T STORE AN EMPTY BATTERY FOR A LONG TIME. If Battery Monitor or macOS display that the battery is almost depleted (you are receiving a warning message that the computer is running on reserve power), you should not leave the battery in this discharged state for a long time interval. Due to self-discharge which affects any battery even if it is not in use, the battery could actually discharge to zero level, and the battery processor cannot prevent this. This deep discharge could severely harm the battery.
IF YOU REALLY CANNOT USE A BATTERY FOR SOME EXTENDED PERIOD, prepare it as follows: Charge, or respectively discharge the battery in the computer until a charge state of 50% has been reached. After that, store the battery at a cool place, e.g. in a cellar. Do not put the battery into a refrigerator, however.
AVOID PERMANENT USE WITH THE POWER SUPPLY. If you don’t use the computer as a mobile device, but work with it stationary, leaving it always connected to the AC adapter, you should regularly (e.g. once in a month) allow the battery a full discharge and an immediate recharge.
In case you are operating a mobile computer with permanent connection to a power supply, it is nevertheless not recommended to remove the battery to protect it, if this is possible with your model. Apple computers will run with only half the speed after that. For further information, please consult the web pages of Apple.