Today (7/6/2010) I removed the *original* batteries from my 1986 HP-11C and wrapped it up for permanent storage in my collection. I used the calculator infrequently over the years, but it was always nearby for a quick calculation. Believe it or not, the batteries still powered it enough for usage today. I am amazed! 24 years on the original set of batteries! Wow!!!
(The image is from *this* site and is not my calc.)
Edited: 6 July 2010, 8:16 a.m.