Back in the late 80’s and early 90’s I would use Duracell 8.4v mercury batteries. They made every pedal sound amazing. Since they were made of mercury, they would hold the 8.4v until they died. In my 74 phase 90’s they would last a crazy long time. I remember buying the last small case of batteries around 1990 and I thing I used the last battery around 1994ish. I wish they would still make them. Now I just use Panasonic carbon batteries in all of my pedals. I figure they were all designed around them, why not use ‘em.