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[OM] Testing 675 zinc air hearing aid cells as mercury battery replaceme

Subject: [OM] Testing 675 zinc air hearing aid cells as mercury battery replacements
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Wed, 29 Sep 2010 07:44:14 -0400
This tidbit is extracted from a message on the Yahoo "camera-fix" list. 
  The preceding conversation had to do with 675 zinc air battery life 
and whether recovering the air holes preserved battery life.

Chuck Norcutt

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I dug into my battery bag and came up with 2 previously used 675 cells
plus 4 unopened cells. The unopened were quite old. The used cells were
equally old. The last time I used one was probably in April when I
picked up an OM-1. The packaging has an expiration date of 1/2009 and
there's "fuzz" growing on all the positive terminals that I wiped off.
The unopened cell voltage is about 1.2V.

The two "used" cells has blue tabs over the holes. I lied earlier when I
said I used painter's masking tape. Turns out I just used the original
blue sticky tab that came with the battery. Anyway I measured both - one
was 0.343V and 1.171V. I took one of the unopened cells plus the 2 used
ones and removed their tabs, letting them sit for 5 minutes. After 5
minutes, all three sat in the 1.35V range.

I now dropped each into three cameras of similar vintage - an original
Canon F1 and two Canon FTb's; verified that the meters were working fine
and let them sit with the meters on and no lens mounted for 30 minutes.
When I came back 30 minutes later, I checked the meter again to make
sure the batteries and meters were still behaving properly and they each
were. I pulled the cells and measured again.

The one I had just opened sat at 1.32V. One of the old cells dropped
down to 1.28V while the other hovered around 1.31V. After 5 minutes they
were all back to 1.35+V.

So what does this all mean? Well, for someone like me who only uses 675
cells for the occasional old-camera film action, tape does seem to
extend the useful life of these little batteries; though I think I
probably went overboard with expired cells. Things might be different if
I left the meter on longer than 30 minutes but I do have other things to
do tonight :) And all bets are off if I had to use them in a hearing aid
where the current drain is likely to be higher and continuous.
-- 
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