A (s)imple, (l)ight(w)eight, battery widget, that doesn't ask for any permissions. Only 22 Kb small so it won't eat up your device storage space. The widget displays battery level in percent. No ads. No permissions. 100% fat free.
This is a widget so you need to drop it on your homescreen it is not an app.
If you like more of those simple, lightweight widgets which only ask you for the permissions they realy need and don't fill up you phone with Megabytes of data even if they need to do only a small job then check out the other SLW widgets.
Open source GNU GPL 3.0
*added "you are doing it wrong" info, for people trying to "start" the widget like an app