Over time your battery loses capacity. So while batteries don't last forever, sometimes reconditioning or recalibrating can help extend the life.
To calibrate the battery on your Apple laptop, you’ll need to perform a full cycle:
Plug in the power adapter and fully charge your 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 is 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 - ignore that message and keep running. At this continue to use your computer but make sure everything is saved.
- When the battery gets very low, the computer will automatically go to sleep.
Allow it to sleep for five hours or more (overnight) allowing any remaining charge to drain from the battery
After the 5+ hours connect the power adapter and leave it connected until the battery is fully charged again.
Once you’ve run the calibration cycle, your computer will have a much better idea of how much power is really left in your battery.