If you paid by debit or credit card, they will look up your receipt and fax it to you. Walmart's email to Casey says you will need the store location, the date of purchase, and the debit/credit ...
If you bought an EverStart battery which is a Walmart house brand, most likely they will honor the replacement and warranty even without the receipt. They will look into the serial number, and the date of purchased and they can quickly look it up into their system even without the original receipt .