Apple Mail app uses much more battery in the background than on-screen. IOS27 iPhone 16e. For example 11 minutes on screen 50 minutes background.
Fetch is set to off, notifications off. I have deleted and reinstalled the Mail App. Now the battery use doesn't display the mail app as such....but puts the data about battery use into 'recently deleted apps'. There is only one email account and that is an Apple account.
The battery health is still 100% 'normal'.