This is a simple open source battery calibration app which needs super user rights.
How does it calibrate your battery? The app resets your fuel gauge and the batterystats.bin file.
Why is superuser required? To reset the fuel gauge it has to write into a /sys/class/ file. This is not possible without superuser permission.
Although APK downloads are available below to give you the choice, you should be aware that by installing that way you will not receive update notifications and it's a less secure way to download. We recommend that you install the F-Droid client and use that.Download F-Droid