An AirTag does not have a rechargeable battery, so once its replaceable coin cell is exhausted, the tracker eventually stops communicating with the Find My network.
Before that happens, iPhone should warn you that the AirTag battery is low. You can also open Find My, tap Items and select the AirTag to check whether a Low Battery message appears beneath its name.
Once the battery is completely dead, the AirTag cannot send Bluetooth signals to nearby Apple devices, which means no new location updates can be relayed through Find My. The app may still show the last location and time at which the AirTag was detected, but that information will become increasingly stale.
The AirTag itself does not need to be replaced. Apple designed it around a user-replaceable CR2032 coin battery. Press down on the stainless steel cover, rotate it anticlockwise, remove the old cell and install a fresh one with the positive side facing up.
After replacement, the AirTag should reconnect without needing to be paired again, provided it is still associated with your Apple Account.
If an AirTag appears to have stopped updating unexpectedly, a flat battery is one of the simplest things to rule out before assuming the item is out of range or there is a Find My problem.
