(Disclaimer: This is my experience understanding and only, so no responsibility can be accepted for readers
trying out battery combinations which may not work as expected or even damage a camera. It is presented
in good faith for Miranda users and collectors  in finding alternatives to the originally specified batteries.)

With the demise of the mercury cell, users and collectors of classic cameras face a real dilemma. Most common
batteries missing are the PX625, PX675, PX400, and PX640. These were all 1.35v types. Many cameras used
the 625 and 675, including Miranda. The PX400 was used in most Pentax Spotmatics and Fujica ST models.
The PX640 was a substantially sized squat battery, powering the electronic shutter in many automatic compact
rangefinder models in the early 1970's.  This included the Miranda Sensoret, but also many quite expensive
cameras from Minolta, Yashica, and others. Without the 640 cell, this type of camera will not work at all.
The Miranda SLR's only used the battery for metering (except the dx-3, using current S76 type batteries),
so they will work happily as a fully manual camera.

There are several alternative means for achieving a replacement:
(1) find a supplier who imports batteries from Europe to the USA. Eventually, mercury batteries are unlikely
     to be available anywhere. I have heard, for example, that production of the PX640 has already stopped
     in some European countries.
(2) Use the replacement cells made by Wein for the 625 and 675. These are good substitutes, but are expensive
     to buy and only have a fairly short life (several months, compared to the two years from a mercury cell).
(3) Recently there has been marketed a 625 converter, which fits a S76 battery inside a 625 shaped holder and
     provides the necessary circuitry to present the correct voltage at the terminals. I think it is about $30 but
     initial tests show it works well.
(3) For the 625, use the replacement 625A battery (1.5v) which is readily available. There are some caveats
     to doing this, including  the possibility of the higher voltange 625A cell burning out the meter circuit, which
    happened to an Olympus RC35 on test, according to Modern Photography at the time. This has not been
    my experience with any Miranda SLR so far, but...

  If the 1.5v cells do work, there are several challenges according to one battery expert I have found:

    (a) you can adjust the ASA to get compensation, but the results will
        probably not be linear over the entire range of the meter. You really
        should re-graduate the meter and record the compensations needed.
    (b) you can adjust the meter internally, but the success depends on the
        flexibility of the adjustment system. In the Sensorex EE, for example,
        there are separate adjustment tabs for high and low light levels. This
        has more potential than others for an acceptable adjustment over the
        whole range. Note: I have not worked with a repairman to find how well
        it works in practice, so don't assume it will work perfectly.
    (c) most of the old circuits using mercury cells were relatively simple in
        operation. The cell kept its voltage very constant until the end of its
        life, when it dropped off dramatically. The metering circuits of the day
        had little need to compensate for a drop in voltage over the life of the
        cell. This is not the case with the current silver 1.5v cells, and part
        of the exposure IC's in current cameras is devoted to this task.
        Therefore, if you use 625A cells, the readings will probably be less
        consistent over the life of the cell than with the older 625 cells.

Apparently some cameras were straightforward to adjust  to 625A (such as the Olympus OM1).

Update March 2000:
To date, several readers have successfully used 625A cells or LR44 cells to replace 675's, halving the ASA speed set for the meter. Feedback received indicates about 1 f stop is about right, but it's much better to test the camera meter against a known meter at different points along the EV range to establish linearity and relative accuracy.

Please continue to email me with futher information or questions about finding suitable batteries for Mirandas !

Another site that has extensive information about these batteries is  for Bronica cameras, but the battery discussion page is:

www.smu.edu/~rmonagha/bronbattery.html#prob

And finally, importantly, we have at this time a supplier of 625 and 675 batteries.

Fred Philibert ( fred@philibert.net ) has kindly advised he does have PX625 and PX675 batteries in stock (for now).
You can visit Fred's page at :   http://www.philibert.net/battery.html

Update July 2000:
The Energizer replacement for the PX625 is a manganese dioxide 1.5v type E625G, details found on the web at http://data.energizer.com.  

Another replacement suggestion... from a correspondent who successfully tried the AC675E battery. This is a 1.4V Zinc-air battery, which is commonly used for hearing aids. You can purchase them in a four-pack for a few dollars. I have used them to replace PX13 batteries for other earlier model 35mm cameras. I would think that the 1.4V would be close enough to the 1.35 to give the same results. These batteries do have a smaller diameter but, I took a faucet washer and cut it to fit the outisde diameter of the battery and the inside diameter of the battery compartment. (The washer keeps the battery centered over the +/- contacts).

I'm also advised that www.photobattery.com has genuine mercury cells, for 10 bucks each, with free shipping in the U.S.

Update August 2000:
Another source for 625 and 675 batteries, this time from Canada:

Henry's Photo Digital Video, a camera store in Toronto. Their website is
www.henrys.com, and they are set up for internet sales to US and Canada.
Their 625's are advertised for USD$4.76, 675's for USD$4.36.
ALSO: Order by phone: 1-800-461-7960 Order by Fax: 1-416-868-0243