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Apple: About Mac notebook batteries - How to optimize the life of the battery in your Mac notebook, fix battery issues, and get service. https://support.apple.com/en-us/HT204054
Understanding batteries in Mac notebooks
Optimizing battery life
Adjusting display and keyboard brightness
Graphics performance and its impact on battery life
Energy Saver System Preferences
Disabling features and technologies that use power
Troubleshooting batteries
My battery won't charge to 100%
The low battery warning doesn't display
Servicing the battery in your Mac notebook
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Hold down the Option key and click the battery icon in the menu bar of your Mac.
Choose Apple menu > System Preferences, then click Energy Saver.
https://www.apple.com/batteries/
Learn more about how your battery charges
It charges fast for convenience and slow for longevity.
Your Apple lithium-ion battery uses fast charging to quickly reach 80% of its capacity, then switches to slower trickle charging. The amount of time it takes to reach that first 80% will vary depending on your settings and which device you’re charging. Software may limit charging above 80% when the recommended battery temperatures are exceeded. This combined process not only lets you get out and about sooner, it also extends the lifespan of your battery.
Learn how to get the most out of your battery
A great place to start when troubleshooting battery issues is the built-in diagnostics that are available on your Mac notebook. Follow the steps in these articles:
If Apple Diagnostics tells you that your battery requires service and cites reference code PPT004, you should confirm this issue by running Apple Diagnostics over the Internet, which uses the latest diagnostic information. To do this, turn off your Mac by choosing Shut Down from the Apple () menu. Then press the power button to turn on your Mac. Immediately press and hold Option-D until Apple Diagnostics begins.
If running Apple Diagnostics over the Internet confirms the issue, contact Apple or take your computer to an Apple Authorized Service Provider or Apple Retail Store. They'll tell you which service and support options are available.
If you don't find any issues with Apple Diagnostics or Apple Hardware Test, read on for more information about troubleshooting your battery.
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Shallow discharges and recharges are better than full ones, because they put less stress on the battery, so it lasts longer. When your battery is discharging, Battery University recommends that you only let it reach 50 percent before topping it up again. While you're charging it back up, you should also avoid pushing a lithium-ion battery all the way to 100 percent.
If you do fill your battery all the way up, don't leave the device plugged in. Instead, follow the shallow discharge and recharge cycle we just mentioned. This isn't a safety issue: Lithium-ion batteries have built-in safeguards designed to stop them from exploding if they're left charging while at maximum capacity. But in the long term, electronics will age faster if they're constantly plugged in while already charged to 100 percent.
Although shallow charges and discharges hit the longevity sweet spot, there are exceptions to this rule. Once a month, let the battery undergo a full discharge to about 5 percent, just to recalibrate its self-assessment. This mechanism allows your laptop or smartphone to give you an "estimated battery time remaining" reading that's somewhat accurate. Regular full discharges aren't a good idea, though. In general, you should be keeping your battery above 20 percent, according to Samsung.