The creator wrote me back
The app wasnt alerting me so I wrote the app and got an email the same day telling me was I was doing wrong. You have to keep the app up while charging, just like every other app and it alerts you just like it says it does. Now that I know what I was doing wrong I use it correctly and it alerts me. Thanks for standing by your app!
Trishluv about
Battery Tune - Full Charge Alarm, v1.5