This month, scientists at Princeton University managed to prove that this test is in fact accurate. Using “non-destructive mechanical testing” (read: dropping), the scientists were able to show that the amount of charge a battery has left is inversely proportional to how bouncy the battery is.

As Scientific American notes, alkaline batteries contain a zinc gel that oxidizes as the battery discharges. The gel gets denser the more it oxidizes, causing it to bounce higher when it’s dropped, like a golf ball on freshly-paved asphalt.

As we all now know, it’s totally fine to throw out most regular batteries, but now you can easily double-check that you’re tossing out the right the ones.

The above image was taken by John Seb Barber and shared under a Creative Commons license on Flickr.

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