Mailbox - do dead batteries bounce?

Adrian asks: why would a used battery bounce on its end more than a full one? Phil Sansom explains...
09 December 2019


A row of double and triple A batteries.


This is the part of the show where we read out some of your correspondence. Adrian has written into our Facebook page to ask: “why would a used battery, double or triple A, bounce on its end more than a full battery? Phil Sansom explains...

Phil - I actually thought this was a really interesting question. In fact, I didn't expect it to be true. Sometimes people say that you can tell a flat battery from good one because the flat ones bounce, but I actually thought it was just a rumour. It turns out though, that scientists from Princeton did a study testing this by dropping batteries down tubes, and the flatter ones do indeed bounce higher, at least up to the point where they're half drained. To find out why they dissected the batteries and saw that at the negative end, which starts out containing a zinc gel. It slowly turns into a ceramic as the battery drains and the zinc oxidises. That ceramic gives it the extra bounciness, so the dead batteries bounce story is half true. The key thing is they might still have half their charge left.

Chris - I think I'll stick with a multimeter though, if that's all right. Probably a bit more reliable, isn't it? And quieter.

Phil - I think so.

Chris - Thank you very much Phil. Well, when you're not dropping your batteries, why not drop us a line to or tweet @nakedscientists, if you've got something you want mentioned here on the mailbox.


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