The stock Android OS does not show battery percentage in the statusbar, if you pull the right side down about were the battery icon is you'll open Quick Settings and the Battery tile will show the batteries percentage.
Alternatively you can install an application like Battery Widget Reborn
from Google Play, ye it can put a widget on your homescreen but it can also place a small battery percentage icon in the right hand side of the statusbar. Like this.
There are many more apps that can place the battery percentage in the statusbar, have a look on GP.
Sent from my 32GB Nexus 7 using Tapatalk HD