If you’re one of those people like me, I don’t like to count on a battery icon to show how full a battery is, I like to see the actual percentage. Out of the box in Big Sur this is not turned on, same as other Mac OS releases of the past. Normally we just click the battery in the top right toolbar and click the check box to enable it. That’s not there in Big Sur, but it’s easy to find.
How To Enable It
Click the apple menu -> System Preferences -> Dock and Menu Bar
Scroll down on the left to Battery, click it, check the box for Show Percentage and you’re all set.