To replace the battery in an Apple AirTag, follow these steps:

1. Press down on the polished stainless steel battery cover of the AirTag.
2. While pressing down, rotate the cover counterclockwise until it stops turning.
3. Remove the cover and take out the old CR2032 lithium 3V coin battery.
4. Insert a new CR2032 battery with the positive side facing up. You should hear a sound indicating the battery is connected correctly.
5. Align the three tabs on the cover with the three slots on the AirTag.
6. Press down and rotate the cover clockwise until it stops.
7. Check in the Find My app on your iPhone to ensure the AirTag is working and does not show a low battery warning.

Important notes:

• Use CR2032 lithium 3V coin batteries without bitterant coatings, as some coated batteries may not work with the AirTag.
• Keep batteries and the AirTag away from children due to choking hazards.
• You will get a notification on your iPhone or see a "Low Battery" warning in the Find My app when it is time to replace the battery.

This process is straightforward and usually takes less than a minute.