Apple states an AirTags' battery should last around one year. However, the actual length of time a battery lasts will depend on the frequency of its use and the condition it's kept in throughout the device's life.
People Also Ask
However, there are a few exceptions carved out in the law. Unless there is a domestic violence protective order or other restraining order in place, hiding an AirTag in your car may be legal, so long as the car is titled or leased in your name or jointly with your spouse.
Batteries, electric and electronic devices. For your own personal use you can take up to 15 battery-operated Personal Electronic Devices (PED) that containing lithium batteries such as laptops, tablets, smart phones, cameras, music players, smart baggage tags (e.g. Apple AirTag).
In checked baggageSmart luggage tags (e.g. Apple AirTag) may remain energised provided the device contains only lithium batteries not exceeding: Lithium metal content must not exceed 0.3g of lithium.
You might not want to attach an Apple AirTag to the exterior of a checked bag -- someone might snatch it off. Hiding it in one of the bag's interior pockets, or attaching via an AirTag holder for luggage, ensures that a bag thief won't be able to locate and remove the tracker at first glance.