My menu bar looks like this:
As you can see the battery icon is missing because I accidentally removed it by CMD+Click+Dragging it off of the menu bar. Also, the customize toolbar button is not clickable.
The simple way, goto "System preferences" -> "Energy Saver", and check "Show Battery status in menu bar"
Go to system preferences and click on energy saver. There, you check the unchecked "Show battery status in menu bar". Your battery should appear.