Silver Oxide cell output characteristics: 386 vs 357.

[BrianShaw]

This question was inspired by another thread where there was mention of output characteristics of MR-9 voltage adapters. It was written that "Also any adapter will not make the the voltage a constant 1.35V like a mercury cell.", presumably intending to include adapter and a silver-oxide cell as intended rather than a lithium cell.

What is a good, cheap handheld exposure meter ?

I have several cameras that have no meter. My dad has a Lentar meter that he bought in Germany in the late 50s. It takes the unobtainium Mercury battery 1.35v. Im not sure how accurate this meter is especially in low light. In these modern times, is there any cheap and accurate hand held...

www.photrio.com

That is not my understanding as some silver-oxide cells have very flat discharge curves, like the mercury cells. But looking at specifications I've noticed what seems to me to be a weird discrepency. The voltage adapters I've used specify 386 silver oxide cell, but out of eitehr necessity or error I've also used 357 silver-oxide cell. Ohysically, the only significant difference between the cells is that the 357 is slightly taller than the 386, which does not allow the battery cap to be fully seated, but functionally it seems to work.

The discharge curves between the 357 and 386 are quite different. Why would that be for cells that are, for the most part, extremely similar? Needless to say, I stopped using the 357 in light meters...

357:

386:

 

[ic-racer]

The scale on those graphs is different. On the Energizer site the graphs superimpose like this. The 357 having a longer life.

 

[BrianShaw]

Good point! There is still also a profound different in the discharge curve which I find curious for what appears to be quite a similar cell, physically at least. I wonder why…

 

[reddesert]

It would help if you said what the source of the discharge curve graphs in the original post was. On the Energizer website, they don't list the 386 (which is maybe one reason you are driven to use the 357), but they do have datasheets for the 357 and a number of other small batteries. For example, datasheets for the 357 and the 395:
https://energizer.com/wp-content/uploads/2023/11/357-303z.pdf
https://energizer.com/wp-content/uploads/2023/11/395-399z.pdf

What I notice about the datasheets is that 1. the cutaway views all show basically the same structure for the silver oxide batteries. 2. the 357, which is larger, got tested at a significantly higher continuous current drain than the smaller batteries, and it has the steadily declining discharge curve as in the OP graph, while the others have a plateau. I think these are linked. If the battery is tested under higher load its discharge curve will be different, and this effect is not linear. I understand the discharge curves in the original plots show only moderately higher test current for the 357, but I think either that's a big enough difference to show this effect, or something is a little off with the test. There is no reason that a bigger pellet of silver oxide should maintain voltage for a shorter time.

Personally, I think people get more worried about the possible non linear effects of those Schottky-diode battery adapters and battery drain than is necessary. Mercury batteries weren't absolutely perfect either.

 

[bernard_L]

Depends where you look. See below "357" discharge curve from

https://media.digikey.com/pdf/Data%20Sheets/Seiko%20Instruments%20PDFs/SR44W_DS.pdf

The plateau is quite more extended than in the plot shown in the OP. Note that according to some sources, SR44W/357 is a high-drain version.
To make the plot below directly comparable with the one in the OP for "357": the discharge current in the plateau is 1.55/5.1=0.304mA, and from the estimated end-of-plateau capacity 115mAh, the time at that point is 115/0.304=378 hours.
I would not stop using "357" batteries.

 

[BrianShaw]

It would help if you said what the source of the discharge curve graphs in the original post was.

Renata battery spec sheets. The curves they present seemed representative of the relative curve profiles of many other manufacturers.