Is a battery needed for updating
From the battery status menu, choose Display Brightness in the Using Significant Energy section.To manually adjust your display's brightness to a comfortable level, use the F1 and F2 keys.
You can also use the F5 and F6 keys to manually adjust your keyboard's brightness, setting it as low as possible while still allowing you to see the keys.To see the health of your battery, hold the Option key and click the battery icon in the menu bar to reveal the battery status menu.You'll see one of the following status indicators: While some third-party apps report on battery health conditions, the data reported by these apps may be inaccurate and isn't a conclusive indication of actual diminished system run time.Once setup is complete, the battery life will begin to reflect the regular activities you perform on your Mac.Your primary resource for viewing battery status is the battery status menu.Enable "Automatically adjust brightness" to allow your display to dim or brighten based on your surrounding's light levels.
You can use the battery status menu to quickly reduce your display brightness to 75%.
Confirm the correct wattage AC adapter for the computer.
A power adapter rated for a lower wattage than is required for the system might not reliably charge the computer.
Click Display Brightness if it's listed under Using Significant Energy, and your display dims to 75% brightness.
Also consider closing any apps that are listed to save battery power.
Here are some settings and steps you can take to get the most from of your Mac Book, Mac Book Air, or Mac Book Pro battery.