1. What about other mercury cells?
  2. How do mercury cells compare to others?
  3. What about the Wein Cell?
  4. What about the MR-9 Adapter?
  5. What about shelf life?
  6. How should I store them?
  7. How should I dispose of them?
  8. What is your privacy policy?
  9. What is your return policy?
10. Do I have to order an entire card?

What about other mercury cells?

Sorry, I have no information on sourcing other mercury cells. This has been the case for a few years now as it seems the 625 is the most popular size so it has survived.

Two other popular sizes were:

• PX400 1.35V: used in the original Pentax Spotmatic and others. Its size is 12mm (dia) x 4mm (h). Since it is only 1.4mm larger in diameter than the PX675 you may want to try the 675 as a replacement. If it fits in your battery compartment then it should work just fine.
  
  *** UPDATE *** The PX675 will NOT fit in the battery compartment of the Pentax Spotmatic.
  
• PX640 1.35V: used in Minolta Hi-Matic E and F and others. Its size is 16mm(dia) x 11mm(h). Since it is only 4.8mm taller than a PX625 I would suggest you place a couple of washers to fill this in. The washers should have no holes and should be placed against the positive side of the cell.

How do mercury cells compare to others?

Simple meters are just a series circuit and will be voltage dependent. More sophisticated ones will be a bridge circuit which is not voltage dependent. I suspect that any camera which uses a single button cell will be a simple series circuit a bridge would take too much current.

From the above it can be seen that mercury batteries were not chosen by the designers at random. They provide the longest life and most suitable voltage drop characteristic of any of the available technologies.

At first sight a zinc-air is the best choice as its voltage characteristic most nearly matches that of a mercury cell. However there are (of course!) a few snags with zinc-air cells. These are:-

• Once the tab is pulled off to 'start' the cell it only has a life of about 2 months whether it is in use or not.
• The maximum load current is determined by the rate at which oxygen can diffuse into the cell, so you will need to make sure that the battery compartment is not air-tight, and also that air can get to the little hole in the cell which is exposed when you pull the tab off to 'start' the cell.
• They do not work well in very dry air.

Silver oxide batteries have a suitable voltage characteristic, but their higher voltage will cause an error. However this will be reasonably constant over the life of the cell so you can calibrate it out by comparing the reading with another meter and adjusting the ASA setting. Their life expectancy is, however, much less than comparable mercury cells.

Alkaline batteries will give errors practically throughout their life and in different directions at start and end. They will also not have an obvious end-of-life point the first you will know is when those irreplaceable shots come out grossly overexposed! They are the least desirable option, although if you shoot only print film the errors may not be significant.

* source: Duracell 'Guide for Designers' and Peter Hardman

What about the Wein Cell?

The Wein cell is essentially a zinc-air type cell with a proprietary electrolyte. It is "activated" by removing a sticker just like the zinc-airs. Once that's done its life can be considerably short. According to its co-inventor, Bob Shell:

"To make them last longer, take them out of the camera when you are not using it and re-cover the air hole with the stick on tab supplied. What kills these cells is the electrolyte drying out, so if you keep them closed when not in use they can last for years.

If you don't do this, how long they last depends entirely on your local humidity levels. Here in Virginia where I live they last from a year to 18 months. In Arizona they may only last a couple of months.

We spent a lot of time (and money) looking for a better way, and there just isn't one right now."

What about the MR-9 Adapter?

This is an adapter designed to take the S76 silver oxide cell and has a built-in voltage regulator to bring the silver cell's operating voltage down to an acceptable level. It typically costs $30. It may or may not work correctly in a given application. You're still faced with the shorter life of the silver cell if all else works.

According to Bob Shell, the co-inventor of the Wein Cell:

"I bought a pair of MR-9's to use in a Gossen Luna-Pro. I was not impressed. For starters, the MR-9 with S76 battery installed is fatter than a PX-625 and when I put two of them in the Gossen's battery compartment, I couldn't screw the cover on. This pretty much ruled out their use for my application. I also tried each MR-9 in a Leica Metrawatt meter and in a Minolta SRT-202. In every instance, I found that the meter needle did not come anywhere near the battery test index line when I did a battery test. Also, the needles wavered quite a bit.

As I have pointed out here previously, I am the co-inventor of the Weincell. When Stan Weinberg and I started working on this project, our first thought was to build an adapter like the MR-9. We tried a variety of prototypes using a wide variety of power sources from alkaline to lithium. None of them worked well enough to satisfy us, so we abandoned the idea. I was quite surprised a couple of years later when the MR-9 was an actual product, one we had decided was impractical."

What about shelf life?

I have several original PX625s which I monitor occassionally for capacity and they're still good after 5 years. So, that's what I tell customers. Note that I've had several customers tell me they also still have 625s in their gear and they're still good after 8 years of intermittent use.

How should I store them?

I suggest you keep them in a refrigerator. I wouldn't recommend freezing them as I'm afraid of any internal condensation happening during thawing.

How should I dispose of them?

You should bring any spent cells to a local recycler who handles mercury. I will also accept them for disposal. Do the right thing and DON'T just dump them.

What is your privacy policy?

We only ask you for information necessary to process your order and to contact you if necessary. We don't share this information with anyone. We may email you once a year just to remind you of our products.

What is your return policy?

Please make sure your application calls for these cells as we cannot accept returns. If you are uncertain about your application just send us a note and we'll see what we can do.

Do I have to order an entire card?

Certainly not. If necessary, we simply cut cards to fill your particular order. The bubble containing the cell remains intact.