The battery has a sticker that gives the shipped-to-store date. It's actually newer than that (since it was probably on the shelf for a month or two), but when you don't have the receipt (I don't), they'll use that to determine the age for warranty. That's 41 months old, and the battery has an 84 month warranty, so it should be good for 1/2 or more off the price of a replacement.
