Replacing AirTag battery and it still shows low battery level.
TL:DR - remove the AirTag from your Find My app and reinstall it.
It was time to replace the battery in one of my Air Tags. After replacing it, it still showed up with a low battery level. I tried several other batteries, restarted the Find My app, restarted my phone and nothing worked. Finally, I thought to remove the device and reinstall it and now it shows up with a full battery.