Zinc-air Cell Corrosion

For reasons that, alas, have little to do with normal age-related hearing degeneration, I’ve been wearing Etymōtic (that should be a long o symbol) MP-915 High-definition Electronic Earplugs (aka, Martian Ear Beetles) when I need a 6 dB boost for normal conversations. The key advantage: a price 10 dB under full-throttle hearing aids.

Anyhow, each one runs for about two weeks on a 312 zinc-air primary cell, so I picked up a batch from the usual eBay vendor. These were short-dated, which let me figure out how long after the rated shelf life they’d be good for, so I know what’s the largest batch I should buy.

One cell arrived with its air vent seal dislodged:

Corroded zinc-air cell

Corroded zinc-air cell

The cell in the middle is used, with several scratches from the contact point inside the earplug. The cell on the right has a good seal.

Assuming a good seal, the cells seem to work about as well as the long-dated fresh cells included with the earplugs.

Although I found several datasheets (Duracell Energizer Rayovac), there seems to be no way to relate the actual cell you purchase to any particular datasheet; the part numbers do not correspond to anything on the package and the nomenclature varies wildly both between manufacturers and within product lines.


  1. #1 by david on 2013-05-12 - 15:37

    It is indeed a long o symbol (at least here on my browser) but it’s supposed to come before the m, not after. :)

    (Have you heard the joke about the old riveter’s convention? WHAT DID YOU SAY? HAVE YOU HEARD THE JOKE ABOUT THE OLD RIVETER’S CONVENTION?)

    • #2 by Ed on 2013-05-12 - 15:47

      it’s supposed to come before the m, not after. :)


      I think that’s a leftover from my blundering around with Unicode non-spacing marks in my attempts to find the long-o symbol. Turns out that you can put an overbar atop nearly anything you like, both before and after the non-spacing character, which makes editing the outcome rather tricky.

      For what it’s worth, the overbar is called a macron and the Unicode symbol for a long lowercase o is U+014D