Just had a pleasant surprise removing these three Duracell D cells from a 'barn find' Bruel & Kjaer sound level meter. When I saw that there were batteries still present in the instrument, I mentally wrote off the battery chamber, expecting it to be corroded to oblivion. However, these three cells, with September 1995 expiry dates are completely leak-free. They're probably at least 25 years old! Comparison with today's corrosion problems suggests that 'they don't make 'em like they used to
.
One cell even still registers 1V on open circuit and will still deliver 1A! The other two measure -32mV and -75mV. Maybe one of our chemists can explain why a thoroughly discharged battery often reverses polarity
Incidentally, the SLM itself, also pictured, which I'd bought only for spares, just needed the mechanical meter movement replacing and it now works and, after cleaning, calibrates perfectly, so is a nice addition to my collection.
Martin