Airtag battery change. Now airtag not seen by my phone.

With the original batteries, my AirTags worked fine. When the app showed the battery levels were low, I change them all. Now the app does not update the fresh battery power, nor does it see the AirTags at all. I have tried moving the batteries in and out several times. That doesn’t do anything. Its as though the AirTags had no power at all but they have fresh batteries. This makes no sense to me. I’ve made sure the batteries fit properly, I’ve made sure that the batteries are fresh. to no avail. I’ve seen similar posts to this. What’s going on?