Unable to determine if your iPhone battery is a genuine Apple part. This could be because the part is non-genuine, not functioning as expected, or the installation is incomplete

This message will also show up, if the battery has not been replaced with a genuine Apple iPhone battery.

The battery of an iPhone 11 and older should only be replaced by an authorised Apple Service Provider, since only they can get the original Apple replacement parts, such as the battery.

This Apple help article has more details about it:

About genuine iPhone batteries - Apple Support

There is an Apple Self Service Repair Program for some parts of the hardware, including the battery, for the iPhone 12, 13 and 14 models:

Self Service Repair - Apple Support

afolabi41 wrote:

Unable to determine if your iPhone battery is a genuine Apple part.

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Apple Support Community Forum

This is Apple Support Community forum, for user-to-user interaction for information & idea sharing between users, if need be, extend support on technical know-how in handling Apple products from more experienced fellow users, This is not the right forum to discuss with Apple Inc.