How long is a new battery's shelf life?

The battery in my 2011 Macbook Air began raising a "replace immediately" alert after 2.5 years of age. I ordered a new one, and waited for the old battery's charge to degrade, but it never did. That was over a year ago. It can still last for about two hours on a full charge. In the meantime, the ifixit battery I bought is still sitting on the shelf in its shipping box. While I continue to wait, is there any danger of the new battery getting "stale" and not working well when I finally do swap it in?