A new study proves that you can check if a battery still has a charge by dropping it

While many of our devices have evolved beyond the battery, there are still plenty of things — from remote controls to handy calculators — that need trusty AA batteries to function.

That means your junk drawer is probably filled with good, old, bad, and dead batteries — but whether they’re usable or not, it’s hard to tell. Until now.

An old wives’ tale held that dead batteries will bounce when dropped on the floor while those that remain fully charged won’t.

And now, a team at Princeton University has confirmed this. As a battery loses its charge, it undergoes both a chemical as well as physical change — so a used battery will indeed bounce.

One end of the battery contains zinc in the form of a gel, which slowly oxidizes as the battery charge is used up over time.

When this oxidization happens, the formerly tightly packed gel becomes a network of tiny “bridges” that make the zinc oxide act like a sort of spring, which in turn gives the battery a bounce, according to the study published in Journal of Materials Chemistry A.

But don’t throw out just any battery that can bounce. The study also found that batteries reach a “maximum” bounce when they are 50% used up and that the bounce height levels off after that, even though more zinc oxide is still forming.

Here’s the GIF the Princeton researchers made of their experiment in action:

“The 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 at Princeton.

For that, you’ll need a multimeter.

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