Reader James Brown
suggested we investigate the widely circulated idea that you can test to see if an alkaline battery is “good” by bouncing it 6" off of a table. The folklore goes that if the battery only returns a small bounce and falls right over, it still has its rated charge. If the bounce is lively, the battery is depleted. Investigating this tip, I discovered that researchers at Princeton University have definitively busted it
. Turns out, this increased bounce-ability does occur, but it’s not a reliable measure of a still-viable battery.
In an article
published March 13 in the online version of The Journal of Materials Chemistry A, the researchers conclude that the bounces increase because the zinc oxide forms tiny bridges within the zinc material, which decreases the mechanical damping of the battery.
“The zinc starts out as a packed bed of particles that all move very nicely past each other,” Steingart said. “When you oxidize the zinc, it makes bridges between the particles and makes it more like a network of springs. That is what gives the battery its bounce. ”
Steingart said that is not too surprising, as zinc oxide is listed as a component to add bounce to golf balls in many patents.
But the formation of the bridges reaches a maximum “bounce level” well before the oxidation of the zinc is complete. That means that the bounce will reach a peak and level off well before the battery is dead.