My iphone showing an unknown battery part why?

A message about a non-genuine part is discussed in this support document: iPhone parts and service history - Apple Support

An Unknown Part message appears if the part installation is incomplete or if the part:

- Was replaced with a nongenuine part (e.g., you had it repaired with a third party service that did not use an Apple component)

- Was already used or installed in another iPhone

- Isn't functioning as expected

If the reason isn't immediately apparent, go to this page to find your nearest Apple Authorized Service Provider (AASP) or Apple Authorized Distributor (AAD) --> Find Locations

How to make a Genius Bar appointment

1. Go to Genius Bar Reservation and Apple Support Options - Apple

2. Go to "Get hardware help".

3. Select your hardware and continue selecting options requiring replacing parts until you see "Bring in for Repair"

4. Sign in with your Apple ID

What does BIU mean?

Hello chetachi163!

Have you had the battery replaced somewhere? If so, was it done in an Apple Store or by an Apple Authorized Service Provider (AASP)?

Not sure what “BIU” means, if it’s important to your post.

Looking forward to your reply!

Who replaced the screen?

More specifically, was it an Apple Store/Genius Bar or AASP?