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[OM] Mallory 640 mercury battery

Subject: [OM] Mallory 640 mercury battery
From: Joe Gwinn <joegwinn@xxxxxxxxxxxx>
Date: Tue, 18 Dec 2001 22:00:27 -0500
At 1:50 PM +0000 12/18/01, olympus-digest wrote:
>Date: Tue, 18 Dec 2001 09:25:26 +0100
>From: "Roger D. Key" <rdk@xxxxxxxxxx>
>Subject: Re: [OM] Battery for Spotmeter
>
>The (Mallory) 640 is a mercury battery that is presumably banned now. You
>could order it from Radio Shack back in 1998 (list archive info via
>google). I have an old Bolex P1 that used the same battery, and I always
>had problems finding a fresh one. I presume that it is 1.35v, but the deep
>format could hide a double battery perhaps. I think that you will need a
>lot of luck in finding one; let me know if you find a source!
>
>Sincerely,
>Roger Key

It's a single cell.  What is the exact type?  The letters fore and aft matter a 
lot, as shown below.


>I just received my Pentax 1/21 Spotmeter from ebay.  I want to replace both
>batteries, one of which is a common 9V battery.  The other battery appears
>to be dead and is labeled "640".  Does anybody know if this battery, or its
>equivalent is still available?
>
>Bill, KG4LOV
>wowens1@xxxxxxxxxxxxxxx


The Eveready E640 (Mallory RM640) battery is mercury oxide, 1.4 volts 
(nominal), 500 mah (at 0.9 volts), 50 mA max current, 0.625 inch in diameter 
and 0.440 inch long.  The voltage slopes badly, but it spends most of its life 
at about 1.2 volts.  

The Eveready E640N (Mallory RM640R) battery is mercury oxide, 1.35 volts 
(nominal), 800 mah (at 0.9 volts), 75 mA max current, 0.625 inch in diameter 
and 0.440 inch long.  The voltage slopes badly, but it spends most of its life 
at about 1.2 volts.  


I would guess that this is the correct cell: The Eveready EPX640 (Mallory 
PX640) battery is mercury oxide, designed for photo use, 1.35 volts, 500 mah 
(at 0.9 volts), 5 mA max current, 0.625 inch in diameter and 0.440 inch long.  
The voltage slopes a bit, starts at 1.38 volts, but it spends most of its life 
at about 1.3 volts. 


The above from the Eveready Battery Engineering Data manual, Union Carbide, 
1976.  (I never throw a handbook away.)


Joe Gwinn


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