Alkaline batteries have an unpredictable drop off in voltage over their life - they start off at 1.5v, but will end up well below 1.35v. Because of the bridge circuit the spotty should be better placed to deal with this than other brands, but I'm not sure if it can compensate for low voltage (others may be able to confirm). And finally, the moment of truth… The MR-9 battery adapter giving the Leica MR-4 the correct voltage. Another PX625 replacement is a zinc air battery. The WeinCELL MRB625 is a custom zinc/air battery designed to replace banned

Voltage - the voltage of the mercuric oxide cell was 1.35v, the voltage of many of the popular alternatives is 1.5v or so Some cameras use a (Wheatstone?) "bridge" circuit and the metering doesn't depend on the battery putting out an exact voltage. Cameras where metering means centering a needle on a short + | - scale (or the LED equivalent), are likely to fall into this category and should work fine with alkaline, silver, zinc-air or NiMH substitutes. Uwe, is the Contarex Super meter like this? and more precisely to these two 101's. Whether you would get the same results cannot be guaranteed by Other meters were designed with the constant 1.35V of a mercury cell as a fundamental assumption. In this case using any other type of cell can cause problems. But different problems with different cameras because of the way the meter is affected by the characteristics of the cell. If the Pentax you are referring to is a Spotmatic F, it should have bridge circuits that compensate for the extra voltage of Silver Oxide batteries without compensation (best not to use alkaline batteries)... if there is a discrepancy between your Spotmatic F meter and another source it may be due to other factors.

Many cameras and light meters were designed for and require a 625 mercury cell: list of cameras and list of exposure meters. Some cameras and exposure meters were designed for 625 sized cells but include voltage regulation circuitry and thus do not require a PX625 to function properly ( list of devices), and so can use the higher-voltage (and less voltage-stable) alkaline (PX625A, 1.5v) or Silver-Oxide (S625PX, 1.55v) cells. Devices without regulation circuitry (or some method of compensating for other voltages) can use Zinc-Air type cells made especially - with the correct 1.35v potential - to replace the mercury cells. Some old cameras and meters (e.g. Nikkormat FTN, Canon Cannonet QL17 iii, Gossen Lunasix 3, Pentax Spotmatic F) used the 625 mercuric oxide cell. Batteries based on this technology are now illegal in many countries and often a replacement is needed. The PX625 (also referred to by other names such as PX13) is a small button-shaped 1.35volt mercury battery which great number of camera models were designed to use. both equally smooth, crisp, and seemed to function wonderfully. Now to the reason for this posting. What battery to use. This copper-made adapter can convert a LR44 battery or 675 zinc-air battery (also known as hearing aid battery) into a PX625. I recommed using a 675 zinc-air battery because its voltage is 1.4v, which is very close to the voltage of PX625, while the volage of LR44 is 1.5v. The light meter is more accurate when your battery has a more appropriate voltage. That is one advantage of using an adapter+hearing aid battery over using a LR625.

the factory are no longer available in the US. I had read online different possibilities. Different people had different opinions. While many said which battery solution was best, and gave general slightest of possible delays at some shutter speeds. Both went to my long time repairman for a CLA (Clean, Lube, &Silver cell with voltage-reducing adapter: the adapters don't contain actual voltage regulators but just a resistor that will reduce the voltage to approximately 1.35V when the current drawn is that of a typical meter circuit. So they'll work perfectly with some cameras in most or all lighting, but not very well with cameras that draw more or less current than the designer expected, or whose current draw changes significantly with the light level. Another mercury PX625 replacement is a zinc air battery. The WeinCELL MRB625 is a custom zinc/air battery designed to replace banned

I'm starting this thread as a place to put information about replacements for the PX625 battery, as this comes up now and again, and having it in one place makes it easy to point to. It would be interesting to know what cameras this is really an issue for, since I've owned a couple of Canonet 28s and they've been fine with the alkaline batteries, whereas the Canonet QL17 iii is reported to need to the correct voltage. Maybe I'm just less fussy about exposure ...... Zinc-air: usually seems to work well but on some cameras, in some lighting conditions, the difference between the 1.35V assumed and the c. 1.4V delivered can put the exposure off by as much as a stop.The mercury cell problem and its solutions (PDF file) by F. de Gruijter. Also discusses PX675 and other mercury batteries. I thought the best solution would be easy to come by. The original PX625 mercury batteries that these camera used from The LR625 is cheap and almost in the same size as the LR625. The only problem is that the voltage of LR625 is 1.5v, which is 0.15v higher than that of the PX625. The difference in voltage may slightly affect the light meter. But in reality, it does not matter much. I am curious why there are so many many posts on the Internet on how to make substitutes for the Mercury PX625 batteries. If you consider camera cost, the lifetime cost of film, chemistry, etc.. that you will pay with this camera is it important to save a couple dollars/euros/pounds on a light meter battery? RPX625 / RM625 / KX625 / HD1560 / 1124MP / Mallory RM-625R / Eveready E625N / Burgess HG-625R / 4370 / 4371 / V13PX / EPX13