---------------------------------------- 1. PX625 mercury cells - how to replace ---------------------------------------- Information compiled by Doug Richardson As at 4 Nov 99 Replacements for mercury cells ============================== The MR clip-on meter for Leica M2/3/4 cameras, the built-in meters in the Leica M5 and CL, all models of Leicaflex... were designed to use PX625 mercury cells. These are now becoming very hard to find both in Europe and the USA. Disposal of used cells is considered an environmental hazard due to the toxic nature of mercury, and the manufacture of this type of battery has been banned in many countries. Although some Leica dealers still have mercury batteries, these are either old stock or batteries made by "no-name" companies (presumably in counties where their manufacture is still legal). You can still buy a cell which is marked "625" and which is the same shape as the old mercury cell, but it uses a different chemical process, and will produce metering errors. The mercury cell was originally chosen for this role because of one special characteristic - the voltage it produces is near-constant throughout the life of the cell (1.34 volts), making it easy to design a meter which would give consistent results with a new half-discharged or near-expended battery. The replacement cells are alkaline (Mg-MnO2) cells. The problem with these is that the voltage in a fresh cell is around 1.8 volts, and gradually drifts down to around 1.4 volts over the operating life of the battery. These levels of voltage produce metering errors - various people have reported errors of half a stop to one stop. Leica users aren't the only folk who need a replacement for the mercury cell. Other equipment affected includes some models of Olympus and Canon cameras and some hand-held exposure meters (for instance the older Gossen Lunasix dual-range meter). Luckily there are several alternatives to the mercury cell. The notes which follow summarise extensive discussion of this topic on the Lieca User Group mailing list between 1996 and 1998. (By the way, in the world of the PX 625, the words "battery" and "cell" mean the same thing - the 625 is a battery which consists of a single cell.) 1) Zinc-air batteries ====================== Varta and Wein are reported to make these. Zinc-air batteries produce the same voltage as the mercury cell, but have a shorter life. You energise them by removing a tab which admits air to the interior of the battery. Full voltage is reached 30 minutes later, and the battery then lasts for two or three months. 2) Nickel-cadmium rechargeable batteries ========================================= A rechargeable version of the 625 cell was available in the 1970s. Known as the DK 60, this may still be available today. In 1997 LUG member Fred Hess reported that these batteries are made by the German company Varta, and that he'd used them successfully in the Lunasix and Microsix exposure meters, and in the Leicameter. Like the alkaline cell, the nickel-cadmium battery has a voltage which declines as the cell discharges. The nominal output is 1.2 volts, but in practice is probably close to that of a mercury cell when the battery is fully charged. Fred Hess gave the following contract details for the US branch of Vatra: VARTA-batteries, 300 Executive Boulevard, Elmsford, NY 10523 - 1202 USA, tel. (001) 914 592 2500, fax. (001) 914 592 2667. 3) MR-9 battery adaptor ======================== A US company called C.R.I.S. Camera Services has produced an adaptor which accepts the small silver oxide battery of the type used in the Leica M6 dropping the voltage to match that of a mercury battery. It is shaped to fit battery compartments designed for the PX625 mercury cell. This MR-9 adaptor is expensive ($29.95 plus $1.50 shipping). Contrary to popular belief, it does not have a voltage-stabilisation circuit - it simply uses a small resistor to reduce the voltage. The amount of the reduction depends on the amount of electrical current the meter circuit draws, and the manufacturer has selected a value suitable for a typical 'moving needle' metering system. In practice it seems to work well in Leica equipment. (It would not work in meters which use LED or liquid crystal readouts rather than a 'moving needle' electro-mechanical system. Electronic readouts would not draw enough current to reduce the voltage.) The phone number for C.R.I.S. Camera is 1-800-216-7579. Their internet web site is at and it lists there the cameras and meters with which the MR-9 is compatible. Recalibration - another potential solution? =========================================== Some people solve the battery problem by having a technician recalibrate the meter for use with alkaline cells. However this doesn't overcome the problem that the slowly declining voltage will create some metering errors as the battery ages. In summary... ============= There is no perfect solution, but enough workable ones to keep older systems operational. (Note: the writer has no business or other connection with any of the companies mentioned above.) -------------------------------------------------------- 2. PX625 mercury cells - latest info & Leicaflex SL use -------------------------------------------------------- Date: Thu, 8 Mar 2001 From: Jem Kime Here's a condensation of previous chats on the SL battery problem. '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. 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. 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: 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: --- A few days later, Marc James Small added this note: Production of mercury batteries has not been "outlawed" in the US. The Environmental Pollution Agency issued a regulation that manufacturers had to ensure that such batteries, though, did not entire the trash stream. Alternatives suggested included a "deposit and return" system (that is, for instance, an initial purchase of a battery might be $15 or so, with $5 being a deposit. Subsequent purchses would be at market price, but would require you to turn in one battery to be allowed to buy another.) The manufacturers declined to make such an arrangement and simply ceased production. Mercury batteries are still in production in the former Soviet Union. --- From: "Earthmother" Subject: [LRFlex] Re: Leica SL metering Date: Mon, 14 Jun 2004 14:43:21 -0400 I've had a Leicaflex SL recalibrated for a silver oxide battery by Sherry Krauter; this was done during a CLA without additional charge so far as I can tell. I'm pleased with the modification. The S625PX cell, being the same size and shape as the original mercury cell, will fit the battery compartment directly. It is possible to use the far more readily available SR44/LR44 (and its clones) silver oxide cell as well. I'm using an O-ring to center the cell in the compartment and a small metallic spacer to make up for the difference in battery height. A bit of bother but these smaller cells seem to be sold everywhere, often at one third the price of the S625PX. The CRIS adapter seems to work well for some people and not for others. I'm in the latter category and found the the SL meter, when using the CRIS adapter, to give readings off by several stops from those obtained with a new mercury battery . I suspect that the meter current draw may exceed the voltage regulation capability of the CRIS adapter curcuit - this seems to be the case with some Nikons as well. --- end