The display on Mary’s favorite little calculator (remember calculators?) faded away and, of course, this appeared when I popped the back:
A touch of vinegar, some scrubbing, and new cells restored it to good health.
That was easy …
Calculator Battery Corrosion
The Smell of Molten Projects in the Morning 
Who could forget the TI-30?
This one is dumber than a box o’ rocks, but it beeps when she pushes the buttons: she likes audio feedback. If I could hear the beep, I might like it, too … [sigh]