AirTag uses a CR2032 lithium 3V coin battery, which is available at most electronic and drug stores. The battery is designed to last at least a year before needing to be replaced. To replace the battery, you need to press down on the polished stainless steel battery cover of your AirTag and rotate counterclockwise until the cover stops rotating. Then, remove the cover and battery, insert a new CR2032 lithium 3V coin battery with the positive side facing up, and replace the cover, making sure that the three tabs on the cover align with the three slots on the AirTag. Finally, rotate the cover clockwise until it stops. It is important to note that CR2032 batteries with bitterant coatings might not work with AirTag or other battery-powered products, depending on the alignment of the coating in relation to the battery contacts. Therefore, it is recommended to buy replacement CR2032 batteries that do not have any kind of coating.