Are NOS cell-phone batteries good?

Battery in S7 Edge is nearing EOL. I can find many aftermarket batteries, mostly via Amazon. The only place I can find actual Samsung batteries appears to be on eBay.

But they appear to be old stock, even if maybe "new". So, as a general question:

Will old, unused cell-phone batteries (6+years old) perform as new (assuming I believe an eBay battery is unused)?

And as an aside, this is intended as a general question regarding cell-phone batteries. Depending how it is listed, I am worried reads/answers/replies won't happen because it has a specific phone listed. I think there should be some category for a generic device