The Battery Bounce Test May Be Leading You Astray

January 6, 2016 | Elizabeth Knowles

Photo credit: John Seb Barber/Flickr (CC BY 2.0)

Don’t throw away your bouncing batteries just yet.

Lifehack videos and lists offering to make your life easier are prevalent around the Internet. However, some of the recommended hacks are more effective and evidence-based than others.

At first glance, the suggestion that you could drop your batteries and see if they bounce to determine whether or not they have any charge left seemed reasonable and based in science. However, recent research out of Princeton University suggests that you shouldn’t be too quick to throw out your bouncing batteries. The bounce test doesn’t gage exactly what it says it does.

As shown in the video below, the battery test claims that dead batteries bounce higher than their charged counterparts. However, "[t]he bounce does not tell you whether the battery is dead or not, it just tells you whether the battery is fresh," said Daniel Steingart, an assistant professor of mechanical and aerospace engineering and the Andlinger Center for Energy and the Environment.

Video Credit: ChemistryWorldUK

"What I really loved about this experiment is that the result holds a lot of scientific importance, but it is also the kind of thing I can show to someone without a scientific background and they can still get something out of it," said Shoham Bhadra, a graduate student in electrical engineering and the Andlinger Center for Energy and the Environment.

What you see in the video isn’t faked; it just doesn’t quite follow what the battery trick suggests. As you can see, a battery will bounce even when 60 percent of its charge is remaining.

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So, what is going on? Using the test in the video and x-ray scans of batteries, the research team determined that the bouncing has to do with a battery’s power production. A chemical reaction occurs inside batteries as zinc changes to zinc oxide. At first, a layer of zinc surrounds a brass core and this ring changes to zinc oxide as the battery is used.

"The zinc oxide begins to form on the outside and it pushes its way to the core," Steingart said. "As you get more and more zinc oxide, and the zinc oxide begins to appear everywhere in the zinc layer, the battery gets bouncier and bouncier." The batteries bounce because “the zinc oxide forms tiny bridges within the zinc material, which decreases the mechanical damping of the battery,” according to a News at Princeton article. The bridges act like a network of springs. However, they reach their maximum bounce level long before the zinc is all transformed and the battery is dead.

So, although this bouncing battery life hack has some science too it, a battery isn’t dead just because it bounces. Remember: you can’t believe everything you read or see on the Internet! 

Read about more popular science myths here.

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