Here is an app which shows the battery level of your phone. Go to windows store and search for battery level. Click on the app and install it. When the installation is done, press and hold the app to pin it to your start screen.
You can also make to show the battery level on the screen lock. To do this, select lock screen from settings and press the + button shown below the heading ‘choose apps to show quick status’. This will show the battery level app on the list. Select this app which will show the battery level on the lock screen.
This app gives some useful information like what is the current battery level of your phone, what is time remaining i.e. how long will your battery withstand.