Yashica Mat 124 Cleaning (4 of 4): Battery Replacement

This is the final post in a series of four related to cleaning my used Yashica Mat 124.  The first post in the series describes the task in more detail and includes links to all of the other posts.

A common complaint with used Yashica Mat 124 / 124G cameras is that that meter is inoperative.  On my camera, the eBay auction stated that the meter no longer worked, but I suspect the seller never even bothered to try a new battery in it.  So, it is often worth asking if they’ve tried the meter with a good battery before you determine that it no longer works.

The problem is that the 124 and 124G are designed to run off a mercury 625 cell (generating a nominal 1.4 volts) that has been banned due to mercury content.  As a result, it is very hard to find 625 batteries for these cameras, and even if you can find one, can you really deal with the guilt of putting poison into the environment?  The replacement 625, if you can even find one, is typically alkaline with a nominal (and unstable) voltage of 1.5 volts, which causes the 124 metering to read incorrectly (too high, I believe, causing under-exposed photos).

The best replacement (chemically) is a zinc-air battery, but zinc-air batteries are not commonly sold in the 625 size.  A readily available alternative is the zinc air 675 battery, that produces the needed 1.4 Volts stably across its life cycle but does not fit in the Yashicamat 124(g) straight out of the box.  The image below depicts this physical difference:

625 mercury battery (left) and 675 zinc-air battery (right)

As you can see, the 625 has a much larger diameter and slightly more height.  There are a variety of strategies to get the 675 zinc-air batteries into older cameras – this great page at KYPhoto describes many of the ways.  Probably the easiest are Wein cells — newer zinc-air batteries with the right size specification.  But, Wein cells tend to be harder to find and more expensive than similar batteries because they are a specialty commodity.

The approach I’ve taken is to adapt a 675 battery to fit the space of a 625 battery — Rick Oleson has a good page on this which is similar to my approach.  The basic idea is to increase the diameter of the battery (by placing a spacer in the battery holder) and increase the height slightly since the 625 is usually held by the lip around the outside (not the positive terminal face) but the 675 does not have the lip.  In the image above, you can see the battery holder on the 124 (which includes a metal screw-in top).  But, where Rick Oleson uses wire, I use one of these and some aluminum foil:

Your local hardware store has a wide variety of faucet O-rings that work great for the spacer with the bonus of well-calibrated size and non-conductivity.  I used a 7/16″ I.D. and 5/8″ O.D. ring and it cost me less than $1 for two of them.

Battery-wise, I spent $6 at my local Fry’s Electronics for a pack of 6 Energizer 675 zinc-air batteries:

The image that started this post shows the materials used.  Just insert the o-ring into the hole in the camera (it will fit snugly), place the battery on top of the foil on the cap, and screw the cap back in.  I found it best to hold the cap up with the camera battery holder upside down keep stuff from falling apart.  The battery goes in snugly and securely and automatically centers itself.

And, the end result is a working match-needle meter:

Note the red needle, driven by the battery and sensor, that you need to line up with the yellowish-green ‘hook’.  Easy, costs less than a buck for the parts and a buck a battery, and works pretty well!

Update:  Well, I spoke a little too soon on things working well.  My meter has been malfunctioning and reading low.  Sometimes, when I open the hood up it does not turn on, and sometimes even when it does work it twitches all over the place.  I need to look into it more, but it is likely either the battery contact (which is somewhat corroded — I originally sandpapered it, but I don’t think it took) or, more likely, the switch in the hood is flaky.  I’ll open it up in the near future and see what I can do.  The camera is so much easier to use when the meter is operable, even if the meter is a little imprecise!

Update #2: (10/25/09) The foil ended up being less than reliable, since it tends to compress over time and it may cover the air holes of the battery (causing inconsistent metering).  Instead, I found a twisted spiral of copper wire (22 AWG) does a good job of spacing the battery without restricting airflow:

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