Changing battery
Will I lose games and the progress when I change the battery in my iPhone 6s?
iPhone 6s, iOS 14
Usually memory is retained during battery changeover unless the Apple Store finds any other fault.
Backup the phone in the usual way.
How to back up your iPhone, iPad, or iPod touch with iTunes on your PC
How to back up your iPhone, iPad, and iPod touch with your Mac
How to back up your iPhone, iPad, and iPod touch with iCloud