I had a warning that the batteries in a couple of my AirTags were running low, so I changed them for brand-new, fresh batteries. The tags continue to work but the “low battery” warnings haven’t gone away - and it’s been three days now.
Did you happen to use batteries with a child-proof butter coating? Apparently these have a coating that can prevent them from working right in AirTags.
If the coating is interfering, then the battery won’t work at all. If you can communicate with it (e.g. tell it to play its chime), then that’s not the problem.
That does seem like a long time. I’ve replaced a few, and the warning seems to resync in at most a few hours. Take them out, and put them back in again?
I have never seen this. Whenever I have had to swap AirTag batteries, the low bat warning on my iPhone went away as soon as the AirTag powered back up after I inserted the new battery.
I have a related issue, my battery went dead because I didn’t change it in time (I was traveling, the AirTag wasn’t), and now no matter what I try, I can’t get the AirTag (with new battery) to connect to the iPhone it originally connected to. The battery is good, the AirTag makes a noise when I reseat the battery, but the Find My app refuses to connect to it.