Low Battery Alert for Mac OS X El Capitan I have Macbook Air, Mac OS X El Capitan.

There is no warning box shown before the battery is near %15, like it did for Mountain Lion. So I can not notice and my computer goes sleep simply when the battery is off.

And even if it did I generally miss it because I use it external monitor attached to my Macbook Air. And because I play Spotify, I may miss the warning sound, too.

Is there warning box for low battery on El Capitan? If not, is there any utility or software that may help for external monitors and even playing music?
Default Warning

The battery indicator in the menu bar will turn red when the battery is low. There will also be a critical low power warning when the computer needs to emergency shut down.

See Apple's About Mac notebook batteries page, in particular this section:


  The low battery warning doesn't display
  
  If you don't receive a warning when your battery has a low charge, generally reported at or under 15%, it may be because the battery menu bar icon is disabled. Follow these steps to enable the battery status menu item:
  
  
  Open System Preferences.
  Click Energy Saver.
  Enable the "Show battery status in menu bar" check box to display the battery status menu item.
  
  
  Note: Portables using OS X Mavericks v10.9 or later display the low battery warning when the battery has approximately 10 minutes of power remaining. Earlier versions or OS X instead report it at 15% or less.


Third Party: Power Manager

Software such as Power Manager can be used to trigger scripts, sounds, and actions when the battery level drops:



More advanced abilities such as stopping music from playing and integrating the warning into your workflows is possible. Battery levels and changes are exposed through Power Manager's AppleScript interface.

Disclosure: I am an engineer who works on Power Manager. So, feel free to ask technical questions about the product.