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Mercury Battery for Pentax Spotmatic

dhrubo gupta , Apr 20, 2000; 04:45 a.m.

Cant locate anyone who stocks this - the old reference is Duracell RM400R (1.35V) - any pointers would be greatly appreciated.


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Terry Carraway , Apr 20, 2000; 07:32 a.m.

Mercury cells are not available for sale in the US. They can still be found in Canada and in some places in Europe.

There are other options, but I am not sure which ones are available for that cell (I use 625's). The other options are Wein cells, voltage converter/adapters, and using alkaline cells (worst idea).

Todd Frederick , Apr 20, 2000; 09:06 a.m.

Here is a site on obtaining batteries from Canada:


And here is a site where to obtain converter rings to use S76 batteries in place of PX625/PX13 1.35 volt mercury batteries for your camera...The OlympusGuy:


The other choice is what Leica M3 owners need to do...use a hand meter.

Best of luck.

jason gold , Apr 20, 2000; 10:53 a.m.

Go to a store that fits watch batteries.Ask for the Bulova 214 or UC/Eveready 387S,silver oxide 1.5volts.Fits perfectly.Voltage doesnt matter due to method of meter.

Gary Watson , Apr 20, 2000; 05:54 p.m.

You should have a look at this nice Dutch site devoted to all things "Spotmatic." Battery issues are well-covered there.


Canadian sources for 400 and PX625 series merc cells are drying up fast.Canadian Quality Concepts no longer seems to be around.I'm finding Varta PX625 stocks are dwindling in the Toronto area, so buy 'em while you can.

Charles Ghent , Apr 20, 2000; 06:09 p.m.

I would like to take this opportunity to get the record straight. We have two contingents represented here on this thread...one says we need to adhere to the 1.35 voltage level and therefore need Hg cells. Another says that because of the metereing circuit, the voltage doesn't matter and therefore we can substitute 1.5v cells. Who's right? I've substituted 1.5v cells freely for a long time now, with no evidence of problem that I know about. What's the reason to stay with 1.35v?

Terry Carraway , Apr 20, 2000; 07:13 p.m.


It depends on the camera. A mercury cell has an extremely flat discharge curve. It stays at 1.35 volts from new to just before it dies, and it dies fairly quickly. Many camera metering systems were designed to take advantage of this and to not have any voltage regulation built in. If you use a 1.5 volt cell, the meter will be off. And if you use an alkaline 1.5 volt cell, the discharge curve is not flat, so the meter starts of wrong in one direction with new batteries, and off in the other direction when the battery is well used. And at some point in the middle, the meter will be spot on. If the camera has voltage regulation, this is not a problem, since it controls the voltage to a given level to maintain the metering accuracy. The silver cells have flatter discharge curves than alkaline, so you can compensate for the voltage difference and be closer to what it should be.

If you shoot color print film, the differences in metering may be masked by the latitude of the film and by the corrections during printing.

WRT the availability if finding mercury cells, Varta stopped production about this time last year. So what is out there is what is left. After they are gone, there will be no more.

Paul Darman , Apr 20, 2000; 11:14 p.m.

There is a site (below) that sells an adapter reported to be pretty good, though I have no experience with it.


It does something to the output of 76 cells making them compatible with meters that need mercury cells.

dhrubo gupta , Apr 21, 2000; 07:41 a.m.

Thanks everyone - seems I have my work cut out for me !

Ashod Martirossian , Nov 28, 2002; 09:55 a.m.

I have found few addresses: You can use an adapter (more expensive but long lasting solution) http://www.classic-cameras.com/PX400.htm http://www.classic-cameras.com/MR-9.htm or get the batteries from: http://www.bergencountycamera.com/supplies/batteries.html I have used myself the last one and was happy with price and great customer service. My personal opinion is to use a battery with a very close (if you can't get 1.35V) but not more than 1.4V and stable voltage, otherwise you will get wrong readings on your exposition meter.

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