This iPhone is unable to determine battery health

That means one of two things.

1. You had your battery replaced by someone other than Apple or an Authorized Apple Service provider or
2. You have a hardware problem.

If the issue is 1, there may not be anything to be done about it. Apple may or may not be willing to replace the battery. If it's 2, you need to have Apple evaluate the phone.

Start here:

Genius Bar Reservation and Apple Support Options - Apple

What do you see on the screen when you attempt to to check on the Battery Health of your iPhone? Which iPhone model do you have? Was the battery replaced recently?

Axel F.