So, I left the house with 95% battery today, hopped in the car and streamed a few songs over bluetooth whilst driving. For reference, my bluetooth is normally running 24/7 (for the watch - also running os3) with no major drain, so nothing unusual there. Skip 10mins into my journey and my phone's at 75%. Check the Battery app - low and behold Spotify has devoured 20% battery in 9 minutes of usage. Beware!