I have a ca 1980 Hasselblad metered finder. It has no model style of any kind on it. My research seems to have it being model PME51. I've inquired on another photo talk site, but seem to favor the credibility on this one. Anyway, my research shows this finder to take a PX28. But that's in 1980. Now, the 544 seems to be the cross-reference for that. But these days 544 is alkaline, which has a perfectly awful voltage discharge curve. So I suppose my question is 2-part. 1) Was the original PX28 a mercury battery in 1980?, and 2) Does the finder have a built in voltage regulator set to say... 4 volts or so, so that a bad discharge curve becomes a moot point? Thank you.