How long can a battery possibly last

I won't bore you with the details, but my best friend from high school has an early 70s Sears Die Hard Daddy bought new in "about" 71 or so. We swapped it back and forth and now he has it. I cleaned it out added acid to it and it was still kickin in the early 90s. Kirk wanted it for a bench decoration so I gave it to him, he drained it and still has it. I am sure he could put new acid in it charge it up and go.