Battery exchange
Can I change a battery from one phone (broken) to another one at the Apple store?
iPhone 8
Question marked as
If an iPhone battery needs to be replaced, Apple or an Apple Authorized Service Providers will place a new battery.
They are not going to remove a battery from a (by you) used iPhone and place it in another iPhone of yours.
The battery can be replaced by Apple or an Apple Authorized Service Provider.
See this Apple article -> iPhone Battery Repair & Replacement - Apple Support
If you are going to replace the battery, read this Apple article: Get your iPhone, iPad, or iPod touch ready for service -> Get your iPhone, iPad, or iPod touch ready for service - Apple Support