Spare non-rechargeable lithium batteries are also forbidden in checked luggage[0]. AirTags are allowed because the battery is installed in a device, though Lufthansa briefly tried to argue otherwise after some bad press involving passengers finding their own lost bags[1].

[0] https://www.faa.gov/hazmat/packsafe/lithium-batteries

[1] https://arstechnica.com/gadgets/2022/10/lufthansa-awkwardly-...