Quote Originally Posted by Jorge Oliveira

I believe I'm the (self nominated) resident old Pentax expert.
Which is your camera's model?

Jorge O
I have one of these too. Mine uses a mercury battery which is now obsolete, however it is my contention that it may be replaced with a silver/zinc of similar physical size. The Spotmatic employs a needle match system which normally consists of a bridge-circuite. These circuits only need a source of current. The exact voltage may not be absolutely required. A few tests could be in order. I base this on a long-time familiarity with similar instrumentation utilizing Wheatstone bridge circuitry and some recent experiments with other meters using similar technology.

Truly, dr bob.

P.S. You do not _have_ to have a meter to use this camera (and many others). The Pentax Asahi Spotmatic is a very good camera. I still us mine.