Spotmatic & Spotmatic F -- Batteries

images39 · May 11, 2024

Looking for help in identifying which currently available batteries would be correct for the Pentax Spotmatic and Spotmatic F. I'm not sure if they take the same batteries. Also, is an adapter needed? There's a lot of conflicting information on the web about this. Hoping someone can steer me on this one...

Thanks,
Dale

Hunter_Compton · May 11, 2024

Though I don't have a Spotmatic, having looked into it a bit previously, my understanding is that while the Spotmatics originally used a mercury battery, because they used either a balanced bridge or dual ammeter circuit, a mercury battery is not a necessity, as they are not sensitive to input voltage.

The original Spotmatic should use a 387 size silver oxide watch mattery, while the F should use an SR44 silver oxide battery (though may need an o-ring to center it in the compartment). I would stick to silver oxide as while alkaline batteries can also be found in these sizes, the silver oxide batteries will have a longer life, flatter discharge curve over their life and are much less prone to leakage.

images39 · May 11, 2024

Hunter_Compton said:
Though I don't have a Spotmatic, having looked into it a bit previously, my understanding is that while the Spotmatics originally used a mercury battery, because they used either a balanced bridge or dual ammeter circuit, a mercury battery is not a necessity, as they are not sensitive to input voltage.

The original Spotmatic should use a 387 size silver oxide watch mattery, while the F should use an SR44 silver oxide battery (though may need an o-ring to center it in the compartment). I would stick to silver oxide as while alkaline batteries can also be found in these sizes, the silver oxide batteries will have a longer life, flatter discharge curve over their life and are much less prone to leakage.

Thanks for this information. So it appears that the Spotmatic and Spotmatic F took different battery voltages?

Hunter_Compton · May 11, 2024

images39 said:
Thanks for this information. So it appears that the Spotmatic and Spotmatic F took different battery voltages?

Different battery sizes, but the output voltage per cell would have been the same.

loccdor · May 11, 2024

One word of warning about the battery door. Don't overtighten it, it can become extremely difficult to open if you do.

mshchem · May 11, 2024

I have a SP500, similar to Spotmatic, OEM used Mercury cell. Eveready sells their 387S, which comes equipped with a spacer ring. Fits perfectly, lasts a very long time. 1.55V silver oxide.

Kodachromeguy · May 12, 2024

images39 said:
Thanks for this information. So it appears that the Spotmatic and Spotmatic F took different battery voltages?

Both the regular Spotmatic (and II, 500, 1000, etc.) and the Spotmatic F originally specified mercury batteries, which were 1.35 volts. This was almost constant for their lifespan before an abrupt drop-off.

Last year (2023), Eric Hendrickson, a US repair specialist, overhauled my Spotmatic F and specifically said to use the 625A (alkaline) cells. He said the meter would be correct. So far, the 625A measures correctly.

beemermark · May 12, 2024

mshchem said:
I have a SP500, similar to Spotmatic, OEM used Mercury cell. Eveready sells their 387S, which comes equipped with a spacer ring. Fits perfectly, lasts a very long time. 1.55V silver oxide.

I also use the 387s. Comes with required o-ring and meters correctly. Keep the o-ring and you find the same 387 butteries in most stores.

Spotmatic & Spotmatic F -- Batteries

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