I’m having the same problem. And we are not the only ones https://www.reddit.com/r/sonos/comments/1eai1rw/has_the_sonos_app_been_draining_anyone_elses/

Here same problem too, app stays even active when deactivate background activities 

There was actually already another post in here about this 

Could anyone with the issue please raise a community post, as apparently they won’t look at it until enough people raise it as an issue.

Hi @James_84, far better than posting here is reporting the power drain directly to Sonos Support. More time and effort, for sure, but posting here is rather hit and miss.

As of yesterday their customer support were claiming they never heard of this issue.  Calling in to repeated report it is essential or it will be swept under the rug for a very long time … I’ve seen issues with Garmin apps battery drain that were never fixed despite posts in forums for more than three years.

I had a chat session with support yesterday, they said they knew about the problem and was looking into it. 

They have looked into it and just released a new app update in the App Store to deal with battery drain (the notes say).