You can find the free version right here: https://play.google.com/store/apps/details?id=com.laudien.p1xelfehler.batterywarner

For now the pro version is adding these features to the free version:
- Stats for the charging curve
- stats for the loading temperature
- quick settings tile (Android 7.0+)

You want to get it for free? Read on...

There are two possibilities:
1. The closed beta. Just write me a mail and you are in. The only condition is that you give feedback from time to time. No feedback not beta.

2. You have an idea for a nice new feature? Tell me and if i like it you will get the pro version for free! You can choose between the beta and the pro version. No other conditions!

This library helped me with the intro: https://android-arsenal.com/details/1/4368
Here you can find the library for the graph (GraphView): http://www.android-graphview.org/
You can find the sources right here: https://github.com/pixelfehler1996/BatteryWarner