電池残量 is a free Android app developed by 21.me. It is a simple utility and tool that displays the battery percentage on the status bar as an icon. Upon powering on the device, the app automatically launches.

With the app, users can tap on the status notification message to access settings for starting or stopping the automatically launched service. The app provides a convenient way to keep track of the battery level without having to navigate through the device settings.

Overall,電池残量 is a straightforward and handy app for Android users who want to easily monitor their battery percentage right from the status bar.