Airtag not reseting and with a new battery

Whats-For-Tea29 wrote:

My question is, will Apple replace my airtag as what I paid for has not lasted 2 years

Short answer: no. The Apple limited hardware warranty, that covers manufacturing defects, is only for one year.

I suggest that you follow 6x6's advice and try another brand of batteries that do not have a bitterant coating.

Try another brand of battery. Some brands have a bitterant coating that interferes with the AirTag; Duracell batteries have that coating.