Re: sell by?
Mystic Megabyte, I think you mean self-discharge rather than internal resistance.
I bought a cheap set of Keter electronic kitchen scales from Argos some 20 years ago, which I use a couple of times a week. The four "Tesco Extra Long Life" alkaline AAA cells they contain, in a natty black and gold colour scheme, have a best before date stamp of June 2001, and the low battery indicator hasn't come on yet...