There are in fact two ways to get this done: One requires you to have knowledging in executing adb commands to your device. However the developers have released a simple APK to achieve this, since most casual consumers might be put off by having to install the Android developer tools and using the command line to tweak settings.
- Download Battery Percent Indicator
Type the following ADB shell commandOnce your device has rebooted, you will have the battery percentage indicator. However the indicator text also appears in white, so you wont be able to see it until the battery level is below the actual text.
adb shell content insert –uri content://settings/system –bind name:s:status_bar_show_battery_percent –bind value:i:1
adb reboot
While this may not be ideal, its likely that Google will finally bring this as a standard feature to stock Android in the near future.
source - XDA Developers