Why my phone has a battery problem
Why my phone said that unable to determine if my iPhone battery is genuine,Apple part
Question marked as
An explanation of that message is in the article 'About genuine iPhone batteries' --> About genuine iPhone batteries - Apple Support
"An Unknown Part message will appear if the battery installation is incomplete or if the battery:
• Was replaced with a nongenuine battery
• Was already used or installed in another iPhone
• Isn't functioning as expected"
Get Apple to examine your phone.