I want to know if there's a battery percent on the update 8.1. I see it in some people's phones but I don't know if they have an app for that or if that's a thing of the update 8.1.
Windows Phone 8.1 has two built-in ways for viewing battery percentage:
In the Action Centre - swipe down from the top of the screen and the percentage will be shown right underneath the battery icon, next to the time and date:
In the Battery Saver app, under Settings:
You can either pin this app to your Start screen or open it from the all apps list.