Indeed fromsomewhere, I found that it is important to close the app. Even to remove it from the memory in my iPhone. Otherwise it will keep on using battery.
There is definitely some kind of design error that keeps the app active in the background. At least I found this behaviour when I am at home, so within the reach of the network, at a certain point I can even feel the iphone getting warm.
It could well be that having the app in memory does not cause a problem when out of reach of the network.
I did not try the spotify playlist thing yet.
The Philips App engineers have some work to do :-)