Similar issue. Had a duralast battery go bad in a diesel pickup. Both have to be replaced. Autozone says they can't find them in their system. There's no reason to try saving their receipts. The ink is so cheap that even if it immediately gets filed its disappeared or became illegible in a month or two.
While the guy was supposed to be looking for my original battery purchase he remarked that the only battery he could find was for my suburban. This means that three equipment batteries , two for another diesel. And two other vehicle batteries are not going to be warranted if something happens to them. That's seven potential batteries and two for sure have no warranty coverage.
If the receipts were of any use that might be of help but I've dealt with autozones cheap receipts before. The only hope I have is I used a credit or debit card to purchase them and can track down a purchase made one to two years ago.
I will be looking for a auto parts store with a real warranty system. It just seems autozones is designed to make warranties difficult if not impossible to verify.
Reason of review: Poor customer service.