Here is an answer from the Leica-Users list (posted with
permission):
from Jem Kime
http://www.lpp.org.uk
'MERCURY FALLING'
Mercury PX625 PX13- 1.35 V are no longer allowed to be
produced in the US or Europe. Those were the only countries
with plants outside Asia. The last plant producing mercury cells
was Varta in Ellwangen Germany. They were ceasing production
in December 1999. The only place where their might still be
production is China, but no-one there can find anything out about
such production.
Alkaline PX625 1.5 V batteries are currently produced and
available. The increased voltage can cause your meter to read
incorrectly, but as long as the voltage in consistent, this can be
accomplished by changing the ISO, or
by a repair facility. Regardless, alkaline chemistry has a different
discharge curve, meaning as the battery ages - its voltage is
reduced.The mercury puts out 1.35 for a long period, but as it
begins to die the voltage drops suddenly. Alkaline batteries put
out 1.5 v then it declines through 1.35 and finally dies. There is
no indication that your battery is putting out, say, 1.2v and thus
your meter is giving you a poor reading. So a meter on alkaline
properly adjusted, will be fine, as long as your batteries are
fresh. The level to which the batteries voltage drop will affect your
transparencies exposure is up to your level of tolerance.
Two common alternatives are the CRIS adapter and the Wein
cell.
The MR9 'C.R.I.S.' adapter uses AgO2 (Silver Oxide) batteries
and their discharge is somewhat similar to the mercury. The
sleeve accepts a common 'Silver 76' battery and adjusts the
output to the correct level through built in circuitry. The size is
slightly taller than the old PX625 so your battery cover might live a
little more proud than it used to. The cost is $30 and delivery
from the US is not a problem.
http://www.criscam.com/mr9b.htm
The Wein cell is an adapted ZnAir cells, the equivalent for the
PX625 is designated the MRB625. These cells were developed
by Stan Weinberg and Bob Shell (editor of 'Shutterbug' magazine
in the USA). They're manufactured in China for WEIN Products of
Los Angeles and marketed by the Saunders Group in Rochester,
NY., available here in Jessops and other stores, around a
fiver a drop. They're supposedly the closest match for mercury
having a voltage of 1.4V and a very similar discharge curve but
with rumours of short life - up to 2 months. The battery also takes
30 minutes to arrive at operating voltage once the tab has been
peeled off. If you buy this cell, when the battery dies, pop it out of
the adapter, and put in a new ZnAir "76" cell. They don't last long
once you open them, but they are quite inexpensive.
LEICA'S RESPONSE AND ANOTHER ALTERNATIVE
A couple of weeks ago I e-mailed Leica info service on the
mercury battery problem for my SL and CL. Their response was
some kind of standard letter, recommending the zinc-air button.
In addition Leica service has bought some stock of mercury
batteries which is expected to last for two years from now (but
they did not quote their price). They did not mention the CRIS
adapter at all.
Particular in bigger German stores, the mercury buttons are now
difficult to find and their zinc-air replacements seem to be totally
unavailable in 625 size, now I search small shops for old stock
of mercury cells. Last week I stepped into a special shop for
hearing aids. The owner understood my problem well and even
said that mercury is better for hearing aids, too. But he had no
mercury and no zinc-air cells in 625 size. At the end he gave me
little "six-pack" of PX675HP 1.4V mercury buttons. He did not
want money. The weird story behind it is that (a) he is not
allowed by law to sell mercury cells, that (b) a photo dealer next
door sold them to me for money, and (c) that on the other hand
some of his clients (war veterans etc.) still get mercury cells for
their hearing aids free of charge from the German government
who seems of have a large stock.
I found that the smaller PX675HP 1.4V works well in both my
Leica SL and Rollei 35 which both have a metal screw-in cover
for the battery compartment. Despite the 0.05V difference to the
PX625 the light meters are spot on. Unfortunately the small 675
cells do make proper contact in my Leica CL or my Yashicamat
124G.
STORAGE ADVICE FROM VARTA
In response to your inquiry concerning optimal storage of the
mercury cell V 625 PX, the electrochemical self discharge in
primary batteries is considerably low. For mercury cells the
self-discharge is between 2% and 3% per year at room
temperature. Under optimal storage conditions, such as
a refrigerator, the self-discharge rate will be slightly slower. A
range of 0?C to 10?C is a good temperature for storing batteries.
To prevent oxidation it is recommended to store the batteries
vacuum-packed, but do not store them in the freezing
compartment, as inner structures of the cell would be destroyed
upon thawing.
http://www.varta.com/
N.B. The web site information should be read with caution, as it
suggests inserting an 'AA' battery into a Leicaflex SL. One would
need either a large hammer or no brain cells to contemplate
this...
HOW ABOUT RECHARGING?
These old 1.35v mercury batteries can generally be recharged,
so if you've got a stash of the things, it now makes sense to do
so for practical, environmental and economic reasons. And
those (silver?) EXP76 as used in the Leica M6 and just about
everywhere else - those recharge beautifully too.
I had forgotten to turn the M6 shutter speed dial back to "B" and
ran the batteries down to the point that the meter no longer
worked. I recharged them in my solar button cell charger and got
another 8 months of use from the things until I made the same
mistake again. And again. I can't say exactly how many
recharges these batteries will take as I'm still using the same
set. If anyone wants info on those button cell chargers, it's item
#BC300 near the bottom of the page at:
http://www.jademountain.com/energyProducts/battery/smallcharger.html
It's very simple and tiny--it hangs in your window and charges
one button cell at a time. I may get 3-4 hours of direct sunlight at
my house, and typically charge a depleted EPX76 for around 4
days or until open-circuit voltage is near 1.56V, same as a new
one. Though great for silver cells, it was especially designed for
mercury cells. It's made in Colorado, and to the best of my
knowledge, there are no alternatives on the market. Shipping
overseas will be a bit higher than shown on the web order form,
but it should still be pretty reasonable since it's so small and
lightweight.
CONCLUSION
In summary, the two straightforward routes are either buying the
MR9 adapter from CRIS (for PX625 use) or buying the zinc air
cells ready made from Wein. The recharging idea sounds
emminently sensible too. First thing though is to ensure that
present supply of available mercury batteries is used up. For
more information useful sites are:
http://acecam.com/magazine/battery2.html
http://www.photobattery.com/index.html
from Jem Kime
http://www.lpp.org.uk
Cheers,
-- John Collier (jbcollier@home.com), March 11, 2001.