Hi Eric.
It seem that you refer to the PME 51 meter prism finder which takes a battery of the Lithium Type, 28 L, it is six volt and the same used for Hasselblad FC cameras.
I am sorry but, I have to disagree with your remark about the meter sysem in the PME51, I have used it to very effect on transpranancy work when the Sekonic 358 is not to hand with good results.