did they beep when you put the battery in?
does precision finding work?
have they updated their location since you did the battery?
the batteries with bitterant (sour coating to keep kids from eating them) sometimes have problems working, as the coating is applied in the same place the battery contacts are in the AirTag. check your battery package, it should mention if it has the coating. Some of the newer batteries have started applying the coating in a different place so it works. If you did get the bitterant batteries, you can clean the coating off with some alcohol.