What is the Battery Status menu on Mac?
If you’re using a Mac notebook, you can quickly see the status of your battery, and find out if an app is using a significant amount of energy.
If you can’t see the battery icon in the menu bar, you need to add it. See Monitor your Mac notebook computer’s battery.
To view the Battery Status menu, click the battery icon 
in the menu bar.
The first line of the menu shows the percentage of battery charge.
The second line of the menu shows the current power source.
The third line says “Fully Charged” or shows the amount of time until the battery is full. This line only appears when your Mac is connected to a power supply. It may take a few minutes to appear.
The fourth line of the menu provides information about energy usage. For example, if apps are using a lot of energy, it says “Using Significant Energy” and lists the apps. If an app is using significant energy but you’re not using it, consider closing the app, particularly if your current power source is your Mac’s battery.
On some newer Mac notebooks, you see
Display Brightness in the menu when the display’s brightness is set to a level that uses a significant amount of energy. If you click it, the display brightness reduces to approximately 75 per cent, which helps to optimise battery use.