This really shouldn't happen for just replacing the AirTag's battery, but of course, anything is possible.
What’s happening here is tied to Apple’s Activation Lock for AirTags. Even though you deleted it from your iPhone, that doesn’t necessarily mean it was fully removed from your Apple Account. For AirTags (and other Find My devices), they remain tied to the account they were originally set up with until you explicitly remove them from the Find My app. This prevents someone from stealing or reusing an AirTag that isn’t theirs.
The fix is to go back into the Find My app on your iPhone and make sure the AirTag is completely removed from your account.
Here’s how you can double-check:
- Open Find My → go to the Items tab.
- Look for your AirTag, even if it shows as “Offline” or missing.
- Select it, swipe up on the card, and tap Remove Item. Confirm when asked.
Once it’s truly removed from your Apple Account, you should be able to reset it and pair it again:
If after this it still says it’s registered to another Apple Account, and you’re sure it’s only ever been yours, then something went wrong with Apple’s activation system. At that point, you’d need to contact Apple Support, since only they can clear an AirTag that’s incorrectly locked.