I doubt an old battery could last that long.  In case it truly has, forget how long it will last.  I can see no value in that.  Take it apart and find-out what it's made of, so we can make duplicates of it.  It would benefit us tremendously.  As others have said,  The largest benefit would be learning how to make a battery with such a long shelf-life.,(reply>), Low discharge, no matter the costs and keeping it sealed and motionless. There is nothing special to it.