Where can I find replacement PX625 Mercury batteries?
The Leicaflex SL, SL2, Leica M5, CL and MR3, MR4 light meters all use mercury PX625 batteries to power their electrical circuits. Although these cells were easy to get in the 1970s and 80s, today they've practically vanished. The reason is that they have been phased out and banned in many countries due to their polluting mercury content. (Oddly enough, for a long time they were still available in Canada and Australia…)
Silver oxide batteries - okay?
Can you use similarly shaped non-mercury batteries instead?…
No - mainly because their voltage profile is different to mercury cells. Instead of maintaining a constant 1.34 volts during their life, non Hg cells vary their voltage over time as the stored charge runs down. As most light meter circuitry was designed to only work reliably assuming a constant voltage power source, variable voltages will thus throw the calibrated electronics out.
Recalibrate to use Silver Oxide batteries
What about having your camera / lightmeter re-calibrated to use newer Silver Oxide cells - possible? For some models, yes it is. In April 2005 Ed Balko sent me the following note:
[…] The cameras that were designed for the mercury cells are getting on in years and would probably benefit from a CLA in any case. Sherry Krauter here in the States will recalibrate a camera in for service at no addional cost.
I use the smaller SR44-sized battery in the original battery compartment using an O-ring to keep it centered and a thin brass washer to make up for the difference in thickness; nothing new here, many people do something similar. These batteries are so easily found that it can be worth the slight bother to install them.
There is also a silver oxide battery, sold here as the S625PX, that is exactly the same size as the old mercury cell. It installs directly in a Leicaflex SL battery chamber. I surprised that more people don't seem to be aware that the S625PX is available. […]
Mercury alternatives - overview
Doug Richardson has compiled a detailed 800-word text summary of PX625 cell alternatives and options. In March 2000 Jem Kime updated it, especially regarding the use of mercury batteries or equivalents in the Leicaflex SL(2) series cameras. He also notes a surprising fact that mercury and silver button cells can be recharged!
This document is too long and detailed to include here, but it is definitely worth reading: click here to read (TEXT 13k bytes).
CRIS MR-9 adapters
All this sounds pretty bleak, but there may be hope on the horizon. There have been numerous claims that 386 silver oxide cells inside CRIS adapters seem to work okay. See the April 2006 remarks by Andrew Touchon about using the combo in a Leica CL:
For more detail about MR-9 adapters, see <criscam.com>.
Problems with the Leicaflex SL?
Although Criscam warn the adapter won't work in the Leicaflex SL, Don Dory reports it works fine in both his SL and SL2. Many others complain however that although the adapter fits into the camera and works okay, it is slightly too large to allow you to screw the battery cover fully closed. YMMV. See this March 2005 discussion at: <Photo.net: #00BQeD>
de Gruijter PX625 adapters
For DIY'ers there are even instructions on the web with how to make your own 625-adapter from a hollowed out PX625 cell. Crazy and downright tricky stuff, but fascinating:
Also, see this detailed PDF document (550 kb).
As of 2005 you can buy battery kits, or even the finished adapters, directly from Frans de Gruijter (€ 5 Euro for kits and € 15 Euro for completed adapters). Paul Birkeland-Green (UK) is also another source.
Here's a May 2004 testimonial by J Gluck Photo:
The CRIS adapter is a problem because you cannot fully screw closed the battery compartment covers. I have a Leicaflex Standard, SL and M5. I'm still working off a stash of PX625s I keep in the refrigerator, but I did purchase two adapters from [Frans de Gruijter] in the Netherlands, who hand makes adapters out of old batteries into which you slip a 1.6-volt silver oxide button cell. They come with a 5-year warranty. The adapter is the exact same size as a PX625 so it closes perfectly. I don't remember what I paid for them.
One of the co-inventors of the zinc-air cell, Bob Shell, remarked the following in December 1999:
Weincells are zinc-air cells invented by me and Stan Weinberg as a replacement for the mercury cells which are nearly impossible to find in the USA. They match the voltage and discharge curve of mercury cells very closely. Unfortunately, they don't last as long as mercury cells, but our feedback indicates that most users are getting about a year out of our latest versions.
Weincells are distributed in the USA by Tiffen and are also available in many other countries. The item to look for is: "MRB625 Wein Cell 1.35v mercury-free-battery"
[Will humidity effect battery life?] Yes and no. The electrolyte is a gel. It uses oxygen from the air in its chemical reaction to make electricity. The gel is water based, and gets air through small holes in the battery casing. When you pull off the plastic tab you are allowing air in the holes to activate the cell. Putting the tab back when the cell is not in use stops the reaction and can prolong battery life.
Since the gel is water based, this means that the cell will work longer in higher humidity since it takes longer for the electrolyte to dry out. Drying out is what kills them. So we have found that life is shortest in very arid climates, longest in very humid ones.
Buying Mercury cells
Face it — they're gone. Kaput. Finished. You can't get them anymore. You'll have to get a PX625 replacement instead. See the following list of dealers: