From the manual: Power source: One 1.3V mercury battery (Mallory RM640, Eveready E640 or equivalent)--for high-light range
One 9V dry battery (Mallory M-1604, Eveready 216 or equivalent)--for low-light range.
I got the manual but never read it in total, what by lack of that meter is quite understandable. But now I am surprised to learn of a meter having two different power sources, for its two ranges.