Availability of batteries: PX-625s (silver oxide)?

[Bill Burk]

We all know why mercury cells were chosen in the first place.

The 625 size batteries are getting harder to find, I would put a washer around a MS-76 if I had to.

 

[GRHazelton]

IIRC Pentax film cameras use a bridge circuit in their meters, so they are able to use silver oxide or alkaline cells and give an accurate reading. Silver oxide is preferable because of its longer usable life.

 

[wiltw]

But are they silver oxide? All my Amazon searches just yield the alkaline versions.

Current search on Amazon discloses no S625PX silver oxide. There are these being offered, which includes the spacers to properly center the 387S (Note: the 'illustration' below serves as a link to that product.)

"Energizer 387S Low-Drain 1.55V Silver-Oxide Button Cell Battery"​

 

[MattKing]

That Amazon listing posted by wiltw looks like it probably would do the job. And if the spacer is reusable, it would be even better, because you would just need the battery itself when it becomes time to replace it.
But why does the listing have to confuse the issue by referring to "1 LR44 battery" (the alkaline versions), instead of silver-oxide SR44 batteries? Probably just a mistake in the listing.
One final caution with these. In a small number of cases, cameras or meters designed for the old 625 mercury cells were designed to make contact with the edge of the battery. For those items, the spacer needs to be conductive.

 

[CMoore]

That Amazon listing posted by wiltw looks like it probably would do the job. And if the spacer is reusable, it would be even better, because you would just need the battery itself when it becomes time to replace it.
But why does the listing have to confuse the issue by referring to "1 LR44 battery" (the alkaline versions), instead of silver-oxide SR44 batteries? Probably just a mistake in the listing.
One final caution with these. In a small number of cases, cameras or meters designed for the old 625 mercury cells were designed to make contact with the edge of the battery. For those items, the spacer needs to be conductive.

Yeah, that IS mice that there is a reusable spacer for those that need it.
It is a bit ironic.....all the talk/worry about the dependability of electronics parts.....that it might be the battery itself is the biggest pitfall.

 

[eli griggs]

You can take an "O" ring that fits about the battery, and some thin, copper or brass or silver wire, wrap some about one side of the ring, say a 6 mm, a quarter inch, and tuck in the tail end.

If you've used copper wire from a device, dissolve the shellac coating insulation on it first, with alcohol and then use as described.

Cheap and effective.

 

[BradS]

Depends on whether or not the Konica's circuits are voltage dependent. Most are, meaning that alkaline cells aren't very suitable.

No. Not for that camera. The original light meter circuit depended on the mercury battery as a 1.35 voltage constant, so the replacement needs to be a cell like the silver ones with a reasonably stable voltage until close to exhaustion. How will an alkaline cell serve this function? Alkaline voltage decreases as it is used.

Amazon warning: beware of counterfeit batteries.

I guess the light meter circuit in the Pentax KX must not care a bit. I've used alkaline, silver oxide and lithium...they all work fine. Although some do better in cold, winter weather than the others. Come to think of it, same is true for the Nikon F2 and F3...and Leica M6. Maybe, it's one of those academic issues that exists but doesn't really matter in real life.

 

[runswithsizzers]

I guess the light meter circuit in the Pentax KX must not care a bit. I've used alkaline, silver oxide and lithium...they all work fine. Although some do better in cold, winter weather than the others. Come to think of it, same is true for the Nikon F2 and F3...and Leica M6. Maybe, it's one of those academic issues that exists but doesn't really matter in real life.

I believe some of the earliest Pentax Spotmatics may have been designed for 1.35V mercury batteries. At some point - possibly around the the time of of the Spotmatic II - Pentax started using bridge meter circuitry which allowed later Spotmatic meters to work with 1.5V alkaline/silver oxide batteries. Certainly, by the time your Pentax KX was made, the owner's manuals were recommending 1.5V batteries.

So for you, yes, maybe it is "one of those academic issues that exists but doesn't really matter in real life." But for those of us who have cameras with meters that depend on a steady 1.35V for accuracy, your assumption does not match reality.

 

[BradS]

I believe some of the earliest Pentax Spotmatics may have been designed for 1.35V mercury batteries. At some point - possibly around the the time of of the Spotmatic II - Pentax started using bridge meter circuitry which allowed later Spotmatic meters to work with 1.5V alkaline/silver oxide batteries. Certainly, by the time your Pentax KX was made, the owner's manuals were recommending 1.5V batteries.

So for you, yes, maybe it is "one of those academic issues that exists but doesn't really matter in real life." But for those of us who have cameras with meters that depend on a steady 1.35V for accuracy, your assumption does not match reality.

I guess I don't understand the angst. Have you analyzed the lightmeter circuit? Have you tried an alkaline cell? I'd try an high quality alkaline, do some tests. it might well be the case that it works fine with negligible to small error for long enough time (a few months maybe?) that you can live with the inconvenience of having to periodically check the meter against a known accurate meter or check the battery voltage periodically. What have you got to loose?

I'm mainly a Pentax and Nikon user but have owned and used Minolta SRT-101 and Nikkormat FTN - both of which use 625 cells. I believe that both were designed to use the mercury cells. I had both modified/calibrated to use 1.5v cells. They both seem to do fine with an alkaline cell. However, I do tend to keep a close eye on the alkaline cells because they bulge with age. I replace them before they bulge - which is long before they're "dead". So...maybe that's why I have not experienced grave inaccuracies. I also do not take what any meter says as the final word but rather as a suggestion....the light meter puts you in the ball park.

I also have owned and used all manner of Spotmatics. Truly, great cameras and fantastic optics. The light meter circuit is designed to use a 1.35 volt mercury cell in all except the Spotmatic-F. All of them work fine as built with alkaline cells.

 

[BradS]

Thank you. It's hard to break through sometimes.

Sorry, I don't mean to upset anybody. Your point is understood and valid....but neither of us has analyzed the light meter circuit. It might very well be voltage dependent but it might also use so little current that the meter is "accurate enough" for an acceptable duration of use. Of course, this requires the user to be vigilant. One needs to periodically check the battery or the light meter accuracy and likely replace the cell before it is "dead". Take the Minolta SRT-101 for example, the circuit is voltage dependent but it also has extremely low current usage and a built in battery check feature. In my experience with the one SRT-101 that I had modified/calibrated to use a 1.5v cell, it was "good enough" for a few months of regular use. Yeah, I had to keep an eye on the battery...not a big deal in my book.

I think it is, at minimum, worth some experimentation. I might work fine. It might work fine for a while and then be off by a half stop at one end or the other (or both). Certainly, it is going to be accurate enough right out-of-the-box with a fresh alkaline cell and there are no catastrophic consequences...so, the question is, how does the accuracy vary with usage? How sensitive or insensitive is the accuracy of the light meter to supply voltage and how does that voltage change with usage (which is related to current draw)? and can the user live with that?

I certainly wouldn't let the apparent non-availability of a silver oxide cell prevent me from using a camera.