When the app is running, the audio engine is also running the whole time. This is done ensure that playback starts immediately when you press play. On my devices the battery drain is around 10%-15% per hour and to be considered normal.
Now when you change to another app and playback is stopped, the engine is also stopped and battery drain should no longer occur. I have seen the battery drain to continue sometimes but I have not found a reason for this and I also see it in other apps like BandHelper. It seems like iOS is sometimes ignoring the command to stop the audio engine.
So if you want to ensure that there is no drain when Stage Traxx is not in use, close it via the task switcher.
