How do I turn it off? – St. Louis Public Radio App Review

I listened for one hour this morning while I worked out. When I finished, battery power had dropped to 90%. I turned off the app and Bluetooth. Five hours later it’s down to 61% and Settings tells me the KWMU app has used 45% of it with “background activity”. How can I stop this? What turns it off?
Review by bills1937 on St. Louis Public Radio App.