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i am an audiologist. this is my go-to method for checking hearing aid batteries on the fly, especially as it lets me work a bit messily.. for better or worse, i

i am an audiologist. this is my go-to method for checking hearing aid batteries on the fly, especially as it lets me work a bit messily.. for better or worse, i now have a habit of ripping fresh batts out out of a packet, without immediately disposing of the old ones i have removed from an aid, while my attention is focused on programming it (older aids often interface using a cable connected to a programming 'pill' which supplies power and data through an empty battery cavity... so i can be putting batteries in and out and programming cables in an out, multiple times in a session with a client... anyhow..) i no longer need to pay attention as to which battery is which, as i just pick up both together and drop them from about a 15cm height.. the old one bounces jauntily away, while the new one stops dead with zero bounce. it is a super accurate trick and the information never fails to astound clients.. it surprised me when i learnt it from an old salt colleague and it surprises me more that it is not common knowledge.. especially amongst my workmates.

londons_explore 3y ago
Hearing aids mostly use zinc-air batteries. I believe your trick works for a different reason - zinc-air batteries get heavier as they discharge since they absorb water from the air.
- eezynow 3y ago
  thanks.. i really know nothing apart from that i enjoy doing it with hearing aid batteries myself.. there is something really satisfying watching the no-bounce battery. as for the reason, i always presumed it was because they take in oxygen. i can't find anything on the weight of discharged vs charged zinc air batteries... but they have always felt a teeny tiny bit lighter when used (i have no evidence!) and i am not sure about your water supposition... i know they -can- swell with water if it is too humid for example, but generally, don't they expel water as they discharge...? "Zn–air battery uses oxygen from the air, and hence, air holes in it are kept open for cell operation. Therefore, loss of water by evaporation through the holes is inevitable. When the water is depleted, the battery ceases to operate. There are two water consumption routes in Zn-air batteries, namely, active path (electrolysis) and passive path (evaporation and corrosion)." source: https://www.jecst.org/journal/view.php?number=300 https://www.jecst.org/journal/view.php?number=300 regardless.. here is a nice video of the effect in hearing aid batteries.. https://www.facebook.com/BMHearing/videos/2037506353043179/ https://www.facebook.com/BMHearing/videos/2037506353043179/ sorry the only link i can find worth sharing is on FB.

londons_explore 3y ago

Hearing aids mostly use zinc-air batteries. I believe your trick works for a different reason - zinc-air batteries get heavier as they discharge since they absorb water from the air.

eezynow 3y ago
thanks.. i really know nothing apart from that i enjoy doing it with hearing aid batteries myself.. there is something really satisfying watching the no-bounce battery. as for the reason, i always presumed it was because they take in oxygen. i can't find anything on the weight of discharged vs charged zinc air batteries... but they have always felt a teeny tiny bit lighter when used (i have no evidence!) and i am not sure about your water supposition... i know they -can- swell with water if it is too humid for example, but generally, don't they expel water as they discharge...? "Zn–air battery uses oxygen from the air, and hence, air holes in it are kept open for cell operation. Therefore, loss of water by evaporation through the holes is inevitable. When the water is depleted, the battery ceases to operate. There are two water consumption routes in Zn-air batteries, namely, active path (electrolysis) and passive path (evaporation and corrosion)." source: https://www.jecst.org/journal/view.php?number=300 https://www.jecst.org/journal/view.php?number=300 regardless.. here is a nice video of the effect in hearing aid batteries.. https://www.facebook.com/BMHearing/videos/2037506353043179/ https://www.facebook.com/BMHearing/videos/2037506353043179/ sorry the only link i can find worth sharing is on FB.