How to play single album on Spotify when bluetoothed? When I am riding in my car I have my android phone hooked up to the sound system via bluetooth. I download an album to the Spotify app my phone at home on wifi because I am cheap and don't want to pay data costs. When I listen to a downloaded album on repeat, then only the downloaded album plays. However, if I do not have the album set on repeat, then, when the album is over, Spotify starts playing something else. Usually it is something on a different album by the same artist. This incurs data costs, which I would like to avoid. So, is this a bug or a feature? How can I listen to a single album with Spotify and have it stop playing when the album is over when I'm hooked up to bluetooth in my car?

(NB: I haven't tried this outside of my car using cellular data, so I'm not sure if that detail is spurious or important.)
In the Spotify app, go to: 
"Your Library" (lower right) -> Settings (cog in the upper right) -> scroll down and turn off "Autoplay". That should do it. Autoplay does exactly what you said. "Keep on listening to similar tracks when your music ends."

You can also or alternatively turn on "Offline mode" at the top of the settings screen. This will only allow the app to play already downloaded songs and will not use any data. You can leave the app in Offline mode for almost a month at a time. They require you to go back online after 29 days to confirm that you still have Spotify Premium and then you can go back to offline mode if so desired.