I replaced the battery in my air tag and now it's not locating it

Double-check the replacement battery to verify that it doesn't have a special bitterant coating that is used to make it taste bad. These types of batteries may not work properly in the AirTag.

Ref: How to replace the battery in your AirTag - Apple Support

No one particular brand is recommended; only that they NOT have the bitterant coating.

You’ll KNOW that you have a “good” battery as the AirTag will beep as soon as you initially re-attach the cover.

Looks like Chattanoogan got back to you, and I would second their response to you.