I noticed that when I left Habit Jewel running full time, my phone would go from almost full to almost empty battery overnight.

This would only manifest after having used the countdown timer, allowing the time to expire so the sound was played, and not having closed Habit Jewel after.

I believe I've tracked this down to the use of gstreamer & pygst to play the countdown timer sound. I have now changed to using /usr/bin/aplay, called via os.system(). No more battery drain for me.