Bruce Varner Photography BruceVarner.com


 

Classic Camera PX625 Battery Replacement

for Minolta SRT101 and Other Cameras 

Updated 06/17/15

This is a tale about trying to find the best battery replacement for a classic Minolta SRT 101.  A black Minolta SRT 101 was my first "adult" camera in 1970.  I recently decided I should again have a Minolta SRT 101.  I ended up with two SRT 101 bodies while collecting the lenses I wanted.  Although both bodies were clean and mar free, they needed new seals and I detected the slightest of possible delays at some shutter speeds.  Both went to my long time repairman for a CLA (Clean, Lube, & Adjust) and new seals.   Upon receiving the camera bodies back I was confounded that they were both equally smooth, crisp, and seemed to function wonderfully.  Now to the reason for this posting.  What battery to use.

 I thought the best solution would be easy to come by.  The original PX625 mercury batteries that these camera used from the factory are no longer available in the US.  I had read online different possibilities.  Different people had different opinions.  While many said which battery solution was best, and gave general reasons why, none seemed to have actually compared the possibilities and provided the results.  This has lead me to actually document my process of finding the best possible solution to this problem.  I have attempted to do that here.

 As I have stated at other times, I am not a camera repairman.  I am not an expert.  I am mechanically inclined and at the time could not find a detailed comparison on the internet. 

 I decided to approach the problem by testing three available solutions.  Testing would consist of comparing the readings from each solution on the Minolta pair, against the readings from my Canon 5D Mark III, and Sekonic Light Meter.  Only fresh batteries were used in all devices for the testing.

 The Three Minolta Solutions Tested--

 1) Duracell recommended replacement battery for the Minolta SRT 101 (PX625ABPK Alkaline Battery, 1.5v)

2) The Paulbg.com adapter ring which is designed to allow usage of a smaller hearing aid battery (ZA675 Zink Air Battery, 1.4v)

3) The CRIS MR-9 which is an adapter allowing a commonly available 1.55v battery to fit into the adapter and when placed into the camera circuitry reduces the voltage output to the desired 1.35 volts (Energizer Silver Oxide 386 Battery 1.55v).

 Methodology--

 --3 different constant lighting conditions were used to compare the exposure results: Strong Light, Medium Light, Lower Light

 --2 aperture settings were used for each test: 1 Stop From Largest Aperture (f4) and 1 Stop From Smallest Aperture (f11)

 --The same lighting scene was used by all devices for each exposure reading

 --The control devices have previously been tested to ensure their relative accuracy

 --Test exposures were recorded with each device at both aperture setting, for a total of 6 exposure settings for each device

 --Both Minolta's used the same MC Rooker 35mm lens

06/17/15 - All three of the below solutions will only work in cameras that compress the positive and negative sides of the battery togather in some form for good contact.  Cameras like the Canon Canonet QL17 GIII have a slot where the battery is placed sideways into an existing slot.  The battery must in these cases be of exact thickness.  Some of the below replacement batteries are thinner than others and thereby may not fully making contact with both the positive and negative sides.

The 675 battery size solution listed below will NOT easily work in a Canonet QL17 GIII.  The 675 is approximately 20 thousandths thinner than the other two batteries and will not work in the Canonet and some others without something to make up the additional thickness, such as aluminum foil.  This also applies to the Wein 1.35v battery........

 Proposed Solutions--

 The easiest off-the-shelf solution, Duracell 625A, 1.5v "Photo" battery.  Marketed by Duracell as a drop in replacement for the Minolta SRT 101 and other cameras that originally used the mercury PX625, 1.35v battery.  No adapter or other modifications required.  Insert into camera and use.

The cost is straght forward for this solution (One Size 625A Alkaline Battery = $3.59)

 

 The second solution for Minolta SRT 101 and similar cameras.  Requires purchase of an adapter ring from Paulbg.com in England.  Said to be a onetime adapter cost as it can be reused repeatedly.  To be used with one of several 1.4v Zinc Air readily available hearing aid batteries.  Here is shown a size 675, 1.4v Zinc Air battery from Walgreens, a pharmacy common in the US.  Battery slips onto the ring, and the setup into the camera.

(Some have used this battery without the above ring by either adjusting the cameral tension or using an O ring or something similar to fill the space)

06/17/15 - If you go to a hardware store and ask for a #9 plumbing O-Ring, it will work perfectly.......

The cost of this solution is (Paulbg Adapter = $7.23ea + Shipping = $2.46 + One Size 675 Zinc Air Battery = $2.12 x 4 for Pack)

 The third solution for Minolta SRT 101 and similar cameras.  Requires purchase of the C.R.I.S. MR-9 adapter.  Also a one time cost as it can be reused repeatedly.  In this unique solution a commonly available 1.55v size 386 battery fits into the adapter.  The adapter is the correct size needed and contains circuitry which converts the 1.55v battery output to the required 1.35 volts that the camera originally used.

This is the most expensive solution (MR-9 = $36.99 + Shipping = $8.50 + One Size 386 Silver Oxide Battery = $1.80)

 Results--

 *Minolta SRT 101 #1 - #2604731.  #2 - #1489639

 ** A + or - character after the shutter speed indicates that the exposure was not exactly centered in the ring.  If the needle was centered in the middle third of the ring, no plus or minus was used.  If needle was in the upper third of the ring I used +, meaning 1/3 to 1/2 stop more exposure was indicated.   If needle was in the lower third of the ring I used -, meaning 1/3 to 1/2 stop less exposure was indicated.

Film Speed 100 1 - 101PX625ABPK Alkaline Battery, 1.5v 2 - ZA675 Zing Battery, 1.4v 3 - MR-9 w/ Silver Oxide 386 Battery 1.55v Control Devices

Minolta SRT 101 #1 Minolta SRT 101 #2 Minolta SRT 101 #1 Minolta SRT 101 #2 Minolta SRT 101 #1 Minolta SRT 101 #2 Canon 5D Mk III Sekonic
Strong Light / f4 1000 1000- 500- 1000 500- 1000 800 800-
Strong Light / f11 125 250+ 125+ 125 60- 125 100 100
Medium Light / f4 60 125 30 60- 60- 60- 60 50
Medium Light / f11 8- 15- 8 15 8- 8- 25 8
Low Light / f4 30 15- 15 15 15 15 25 25
Low Light / f11 4 2- 4 4 2 4 4 3

Conclusions--

 I was surprised how little exposure difference the three solutions made overall.  Before a studio photographer jumps in and states that a 1/3 to 1 stop difference is important, I would like to add that this can be compensated for.  With the Minolta you can adjust the film speed ring by 1/3 of a stop.  By understanding how the battery functions in your camera, exposing a test role, and then for all future exposures adjusting the film speed setting on the camera accordingly, a person can have correct exposures that are as accurate as the camera metering system is capable of achieving.

 The Canon 5D Mark III and the Sekonic light meter were both almost exactly in sync with only minor differences in a couple of spots.  I think that this can a attributed to some differences in the light gathering area between the two.

 I will let people look at the data and draw their own detailed conclusions.  The number of times that test camera 1 had the lower exposure compared to test camera 2 were too similar form me to draw a conclusion as to which camera underexposed throughout the test.

 The number of exposure differences between the two test cameras did drop with each solution that was closer to the factory required 1.3 voltage

---1.5v solution had exposure differences between cameras on every comparison

---1.4v solution had 4 of 6 exposure comparison differences between cameras

---1.35v solution had 3 of 6 exposure comparison differences between cameras

 The four times that the exposure differences between the 2 cameras was more then 1 stop difference might be explained by slight changes in the lighting between test shots.  I did not use a studio setting for the tests.  Exposures were conducted in the daylight, ensuring that no cloud cover occurred during the test shots.  That is not to say that a high thin cloud could not have passed in front of the sun during one or more exposures.......

 Battery depeletion curves were not taken into consideration for these tests.  There are other sources out there that provide drop off curves for the batteries in questions.  It is something that needs to be considered.  The reason that the camera manufacturers went with the mercury battery is its sharp drop off shoulder.  That battery would remain at or near the 1.3v output level until just before it went dead.  The other batteries tested here however have a different curve and would likely start out with the full voltage, but would slowly fall until unusable.  This is another factor that must be considered in your choice.  I personally removed it from the equation by factoring in the decision I would ensure I always placed fresh batteries in the camera every time I used it.

Bottom line to me is that I think a person could successfully use any of the three solutions to power their camera exposure meter if they are carful.  There is significant cost difference between the solutions.  It is close enough that each person will have to make up their own mind which path is best for them.

 I hope you enjoyed the comparison.

 Bruce Varner

 *Caution - The results above only apply to the Minolta SRT 101 and more precisely to these two 101's.  Whether you would get the same results cannot be guaranteed by the above tests.  Fair warning!

 

 

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