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Mercury Battery
by Margaret Mak

Many cameras from the 60s through 80s use mercury batteries. Why? Because the voltage remains stable even if the battery has been partially drained. As you might have noticed, mercury batteries are banned in the United States due to environmental safety. Varta, a leading battery manufacturer, officially announced the discontinuation of mercury batteries in December of 1998 due to European safety laws.

Varta V 625 PX (PX625) Battery

UH-OH, then we should throw all our cameras away that use mercury batteries since the batteries are not available. NO NO NO! There are still many alternatives and replacements for these batteries...

Mercury Battery
These are actually still available in some countries like Europe and Asia. If you're lucky and have a friend in these places you might want to check with them and see if they can dig you some. I've actually seen some for sale in California camera shows too. They are in the price range of $2-$5 each.
Wien Cell
These are zinc-air batteries that are environmental friendly. It's the only replacement out there that is closest to mercury batteries having the exact voltage and stable output. $4-$5 each. These are available at Micro-Tools, Freestyle Sales Co., and Vintagebatteries.com (specializes in the Wein cell replacements with free shipping) just to name a couple places.
MR-9 Adapter
This is an adapter to use in cameras that uses the PX625/PX13 batteries. Regular silver oxide button cells are used and voltage is said to be constant. The only downfall is the price; they are $29.95 each so if your camera uses 2 then you have to get two adapters. But it can be reused many times so it's a "one-time" purchase. Check out C.R.I.S. Camera Services for this product and a list of meter/camera compatibility. If you have a Nikon F Photomic meter, you may not benefit from the MR-9 adapter, instead, you may need the brass adapter available here: paulbg.com
DIY PX625 Adapter
If you like to build or make things, this might be a fun project. See How to make a PX625 battery adapter
Repair Technician
They can recalibrate your camera/meter to accommodate readily available silver oxides. But price...??

These batteries also work but at your own risk...

Silver Oxide Battery
Find the similar voltage and make sure it fits in the battery compartment. You might be able to find the exact voltage, check out hearing aid batteries.
Alkaline Battery
Duracell has replacements for most of the mercury batteries, but voltage varies. For example, PX625, Duracell numbers it PX625A and instead of 1.35V it is 1.5V.

Higher voltage may cause damage to the meter in a particular model/brand camera. Always try to find the exact voltage or the other alternatives listed first.

A Tip About Batteries

For some cameras, the voltage of batteries does not have to match exactly. For example, the PX625 which is 1.35V but regular silver oxides are 1.5V. It may cause a slight difference in the meter readouts but turning the ISO/DIN dial can compensate it. And don't forget that print film has a wide exposure latitude so +/- 1-2 stops is acceptable.

Regarding about the PX32 mercury battery that Yashica Electro's uses, I use 4 LR44 1.5V silver oxide button cells and tape them together. Wrap the batteries with a cardboard so it fits snuggly in the compartment. They work, but I needed to bend a paper clip in order for the end contacts to touch.

Useful info on batteries - submitted by Weyman Swagger

I have been able to successfully substitute 1.4 volt zinc-air hearing aid batteries in equipment that was designed for the 1.35 volt mercury batteries such as PX13 and 625.

The batteries I'm using are designated 675. They've worked in Nikkormat, LunaPro, Kowa se series, Fujica, Minolta, and both Canon and Minolta rangefinder cameras. They tend to last at least 2 months. The cost is about 90 cents per battery in my area, Baltimore, MD, USA.

Since the batteries are smaller than the originals, I shim them into place using rubber O-rings from a hardware store. Because of small differences in battery compartments, I use two sizes of O-ring. In the LunaPro I use one of each.

Here are the specifications of the rings I've used. Certainly others may do as well. First, 5/8 inch outer diameter X 7/16 inch inner diameter X 3/32 inch thickness, called a # 9 O-ring at my local Home Depot store. The other is 9/16 inch outer diameter X 7/16 inch inner diameter X 1/16 inch thickness, called a # 41 O-ring at my local Home Depot store. Price of the O-rings is about 20 cents ($ 0.20 US) The O-rings should last for many years.

After installation, if there is no battery response, I add a tiny amount of thickness and electrical contact to the battery by using a couple of folds of metal foil from a cigarette package on the top of the battery.

In every case where the meter still works, this method has been effective 100 per cent of the time. The meters have been accurate, giving the same results as my Pentax spot meter.

It's a convenient and inexpensive way to get old built-in meters working.

The battery information is well known. I hope the specific O-ring information can be useful to your readers.

Batteries for Canon EF - submitted by Bill Lammers

I have been using your page on how to use hearing aid batteries with adjustments and adapters to replace the old mercury 625 cells. Thank you for providing that information.

The use of the rubber o-rings was working pretty well on older rangefinder cameras that had the battery inserted sideways, but I was getting frustrated because it didn't seem to be working on a Canon EF that I had picked up on eBay. This camera takes two of the 625 cells on the bottom, but they are held in the camera with the positive side up and the negative side down rather than sliding in sideways.

Of course, whenever you get a new old camera, the first thing to worry about is whether the meter works, so I was using the o-ring method to test the camera but nothing worked. I tried putting metal spacers in to make the connection tighter, but that didn't help.

Then I took a long look at the original mercury batteries and found that the metal forming the battery's jacket on the positive side was continuous around the sides until curling inward on the negative side. I started to wonder whether the contacts in the battery chamber were really using the top of the positive side for making electrical contact because the rubber o-ring
was breaking the connection to the sides. I took a chance and wrapped a little aluminum foil around one part of the o-ring, then put the battery back in. Voila! It worked.

I realize that I could easily have used the new alkaline 625s because the EF has a voltage regulator, but I ended up using two 675 hearing aid batteries at 50 cents each (sale at CVS, two eight-packs for $8) and two o-rings (39 cents each) instead of two 625s, which cost $5 each.