Problem with iphone SE battery

This message can appear for several reasons, one them being a non-genuine battery has been installed. But, the same message can also indicate a possible problem with the original battery in the phone.

Make an appointment at the Apple Store or take the phone to an authorized Apple service shop to let them run some checks and tests on the battery.

You can find a list of authorized service shops in your area by using this link......Find Locations

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"

Good luck!