tl;dr: Reinstall the Fitness App
Problem Description
I had problems with battery drown of my IPhone for a couple of weeks. Updating did not fix the issue. The phone got pretty warm and a full battery load lasted for something like 4 hours.
Investigation
The standard ways to fix battery drown were not working. So before resetting the phone I wanted to have some insights what might go wrong.
CPU Load
I had a look at the CPU load of the iphone.
Therefore install Xcode on a Mac and entered Developer Mode on the Phone. The tile for enabling Developer Mode on is only visible when the phone is connected to the Mac.
Then select Instruments in the Xcode Menu and picked the IPhone.
The load diagram showed that every 5 seconds a process called fitcored spawned and exited after a couple of seconds again.
Next step was to invesigate the IPhone’s logs. This could be done by opening the Console on the Mac and selecting the phone on the left pane.
The logs showed following error message every 5 seconds.
Error: unable to create application proxy fore qureying alpplication install state: Error Domain=NSOSStatusErrorDomain Code=-10814 "(null)"
fitcored seems to be related to the Health and Fitness app somehow.
Fix / Workaround
During the last cleanup of apps and data I might have deinstalled the Fitness App. I reinstalled it. Afterwards the warnings did not show up in again and CPU load was okay again.
I opened a feedback at apple.
Summary
My battery drown is back to normal. After 2 hours of moderate using (listening to music, scrolling through a couple of websites, writing some messages), battery consumption was around 3%.
And I learned how to read the IPhone logs and traces.