Battery replacement privacy issue
It appears that an Apple technician cannot replace your iPhone's battery without being logged into your iPhone at the time, which means that a stranger has full access to your analytic and personal data when you aren't even present. And while the technician may claim that no employee in the store ever looks at your data, I see no mechanism in place that would actually prevent it from happing.
If Apple want to live up to its reputation of caring about user privacy, why not simply have an alternate password for diagnostics only, which you can give to the technician?
iPhone 6, iOS 10.2.1