As an alkaline battery is discharged, the anode undergoes oxidation from Zn to ZnO.
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Bhadra, S.; Hertzberg, B. J.; Hsieh, A. G.; Croft, M.; Gallaway, J. W.; Van Tassell, B. J.; Chamoun, M.; Erdonmez, C.; Zhong, Z.; Sholkapper, T.; Steingart, D. A. The relationship between coefficient of restitution and state of charge of zinc alkaline primary LR6 batteries. J. Mater. Chem. A. 2015, 3, 9395–9400.
Caveat from Do dead batteries really bounce? | Office for Science and Society - McGill University:
while it’s true that dead batteries bounce, so do half full batteries, and even 99% full batteries. All this test can really tell you is whether a battery is brand new or not.
That’s a good caveat. I’ve never taken out a half-discharged battery though. I’ll just end up with a few batteries on my desk where I can’t remember if they came from the box or the device.
