Apple - I removed the battery icon from the menu bar. How do I add it back?

The simple way, goto "System preferences" -> "Energy Saver", and check "Show Battery status in menu bar"

You can find the battery.menu among others in the

/System/Library/CoreServices/Menu Extras

double click on it to get it back in the menu bar.

Or more simple way, just enable it in Energy saver as Show Battery status in menu bar.