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Pentax SP500

 
I can confirm that a silver oxide SR41SW or equiv.,used with a 7mm internal x2mm O-ring will work.
 
I bought a Spotmatic F, with f1.8 lens, at a garage sale for $5 USD, a few years ago.
I found that the contact for the meter battery had corroded away.

No problem. I just pretend it's an H3!
 
387S is a 394/380 with an adapter ring
Any battery that is 3.6mm tall will work with an o-ring to stabilize it

The beauty of the 387S is that it comes from the factory with the little plastic "shoulder". It it fits the Spotmatic battery chamber perfectly straight from the manufacturer.