There's no shortage of battery monitoring applications in the Play store. These apps each offer different solutions when it comes to viewing your battery's percentage. Some add an icon to the status bar, others can place a widget on your home or lock screen, and some even place a permanent notification in the notification shade. While all of these solutions work, none are ideal.
Android should support this natively, without requiring a third-party app; I know I'm not alone in thinking this. Thankfully, it looks like Google is finally working on adding a battery percentage feature to Android 4.4 KitKat devices, but it doesn't appear to be quite complete yet. According to a post on Android Police, the feature can be enabled with the use of a single ADB command, or by installing an app -- both methods being possible without rooting your device.