Dead Batteries Definitely Bounce

A team from Princeton University proves how and why batteries bounce when used.

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Batteries are the kind of thing which accumulate in drawers, junk piles and forgotten crevices.  It always seems no matter how hard one may try, new ones and old ones get mixed up, and even if one owns a battery tester, it’s almost never on hand when you need it.  Have you ever heard the rumor that dead batteries bounce?

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The rumor which was deemed to be a simple test to see if a battery is flat or not seemed too simple, too ridiculous.  While it has been met with a degree of skepticism it turns out that there is some truth to it.  Researchers at Princeton University have published a peer-reviewed study in the Journal of Materials Chemistry.

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What their study shows is that the more a battery discharges, the greater it will bounce.  They measured it by dropping batteries down tubes and recording the bounce height.  There is a catch, however;  the bounce ability of a battery reaches its peak and levels off when the battery is half used.  This makes the technique slightly less useful, but it led the authors of the study to find out just why and how the batteries are exhibiting this curious nature.

Basically, it has to do with the chemical components (zinc and potassium hydroxide) which make up the battery.  As it generates electricity, various chemicals react to form zinc oxide and manganese oxide.  The juice stops when there is no more zinc to react with to create the flow of electrons.  The team at Princeton dissected batteries and examined them with a scanning electron microscope.  This showed them that there were physical changes besides the purely chemical ones previously known.

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Within the moist paste with zinc particles, zinc oxide forms around it like a doughnut around a hole;  the gel becomes a ceramic.  The oxidization process forms bridges between the packed particles making a network of tiny springs.  That is what is producing the bounciness, (zinc oxide is also an ingredient for golf balls).  So, while bouncing your batteries won’t tell you if its anything but more half charged, it’s still mildly useful when trying to determine which batteries are pretty good when you got a jumble of them.

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