How much battery have you got left on your phone? 75 per cent? 50 per cent? Perhaps 10 per cent? Without opening the notification area, finding out with a quick glance is simply out of the question.
While Marshmallow owners can enable this in Settings>System UI Tuner>Show embedded battery percentage, and rooted users of older versions can employ the Xposed Framework to add a percentage battery label, those of you without root or Android 6.0 may feel left out.
A quick trip to the Play store will unveil Battery Percent Enabler; once enabled and configured this will fix the problem. Simply run the app and tap the Enable Battery Percent option, ensuring the box is ticked. You can then exit the app to see the value displayed on your battery (some users may need to reboot the device before this happens).