Archived posting to the Leica Users Group, 1999/06/18

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Subject: Re: [Leica] Mercury, Alkaline, and Silver Oxide Batteries
Date: Fri, 18 Jun 1999 18:17:33 EDT

In a message dated 6/18/99 5:45:44 PM Eastern Daylight Time, writes:

<< Mercury have a constant 1.35v even as they expend their energy.  This
 constant is why they were the prime choice in many cameras for metering
 systems. They also have a 10+ year shelf life where as Alkalines are
 generally 1/2 that at best.
 Alaklines have a 1.6+ volts even though they indicate 1.5v per battery with
 the drop off curve being slow and steep.  At the end of their life cycle
 they will generally test about 1.35v where the mercury battery would
 normally be.
 Silver Oxide are a bit in the middle at around 1.55 volts.  They offer more
 constant output, a linear drop off (not steep) and will provide a somewhat
 longer life than alkalines.  Silver Oxide batteries offer a longer shelf
 life than Alkalines. >>

Evidently then it is because Silver Oxide batteries are closer in discharge 
characteristics to the Mercury batteries (and basically just a series 
resistor is needed to adapt them) this is why the CRIS adadptor uses the MS76 
(aside from the lucky fact it's also smaller than a PX13/625 and fits inside 
an adaptor).  The big question is, why do the battery manufacturers only 
supply Alkalines in the PX13/6225 size, and not Silver Oxides?  BTW I had a 
lot of trouble wiith those Zinc-Air Wein cells "replacements".  Not only are 
they expensive, but they go dead in a big hurry.  That is, if they're not 
already dead when you buy them, which was what happened to me.  I finally had 
my Nikon FTn "converted" to take alkalines (this was before I'd heard about 
the CRIS adaptor) but dealing with the discharge curve is a royal pain.  I 
rarely use the F any more, and if I do I have to check the meter against a 
different body at intervals and change the EI.