Apple says the AirTag battery lasts about a year. When the time comes, it is very easy to replace the battery. AirTag uses a CR2032 battery, the type of battery commonly found in remote controls and other handy devices. You can find them at most stores that sell batteries and they cost a few dollars each.
Apple has posted a support document pointing out that CR2032 batteries with a bitter coating may not work with AirTag. (Some CR2032 batteries have bitters added to prevent small children from handling them.) Please check the battery packaging before purchasing. (Hat tip for The Loop.)
In this video you will learn how to replace the AirTag battery. The instructions are listed below.
Open the AirTag by placing the white base downwards. The Apple logo should be facing you.
Press two points next to the logo with two fingers.
Turn the cap counterclockwise. Once the cap is turned, you can remove it and replace the battery.
Replace the cap and turn the cap in the opposite direction to seal.
For more information about AirTag, read our AirTag FAQ and watch a video on how to set it up.