My old HP-35 calculator, the original floating point RPN (reverse Polish notation) scientific calculator, from 1973 is still working. 30 Years+ used daily and still going strong. I will be really unhappy when it quits. One of the best investments I ever made.
I had to remove the battery pack and install a capacitor across the terminals to filter the output of the AC adapter.
I heard that they are now "collectors items". One is in the NY Museum of Modern Art permanent desingn collection. To me it is just a really good tool.