
My Mac mouse is named "Al's mouse", and my Mac mouse battery level is currently 51%. To see your Mac mouse battery level, do the same thing: Click the Bluetooth menu, find your mouse on the menu, and hover over that item.

When you hover over that item you'll see your Mac keyboard battery level (mine shows up as "43%"). On that menu you can see your Mac keyboard battery level by clicking that icon, then scrolling down to your "keyboard" menu item (mine is named "Al's keyboard"). (This is something like the normal Bluetooth icon, but a little different.) This menu will be in the upper-right corner of the Mac menu bar, and it looks like three small dashes with some other figure behind those dashes.

The easiest way I know to see the Mac keyboard/mouse battery level is to put the Bluetooth menu on your Mac menu bar, and check it from there. Mac mouse/keyboard battery FAQ: How can I check the battery level of my Mac mouse or Mac keyboard?
