Percentage of the Battery is not shown by default unless you make some tweaks to get that displayed. Here are few steps to do that.
Swipe the screen from the top and keep pressing the settings icon, it will take you the Settings screen where you can System UI Tuner as shown in the below screenshot. Tap on the System UI Tuner and you get the next screen, tap on Status bar and scroll down.
Tap on Battery, then on the next screen again tap on Battery where you get three options, select Always show percentage which will start showing the battery percentage at the top of the screen.
The other options are Show percentage when charging which is a default one, and Don’t show this icon will not show the battery icon at all.