Since a few days my battery of my iPhone 8 (iOS 13.5.1) drains at a rate of approx. -25% every hour.
Under my iPhone Settings > Battery I noticed an extraordinary background activity (several hours) of the Music App, without being used/opened.
The following preliminary actions did not solve the problem:
- forced restart
- deactivation of background app refresh
Now by coincidence I found out, that each time I close and re-open the Music App, the SHUFFLE-mode is ACTIVATED with another song loaded.
Therefore I have a strong guess, that whenever you close the Music App, music is played continuously in SHUFFLE-mode in the background without noticing resp. hearing it. As soon as I leave the Music App on, deactivate the SHUFFLE-mode and keep the music stopped from playing, the battery drainage resumes to a normal rate.