I've been enjoying listening to Spotify music on my Nexus 4 (running KitKat 4.4.2) since they made it available for free. Only problem is that, in my car, the music stops playing after a couple of songs unless I keep the screen on.  Is this because of the app or the phone?  Does the free version limit the number of songs that can play continuously?  Or does this have something to do with the phone's power settings, the phone goes to sleep when the screen is off?  Is there any way to keep the music running?