Guitar pedals in general, but Fuzz pedals in particular are very sensitive tonally to how they are powered.
Tone hounds and tone connaisseurs agree that most Fuzz pedals sounds vastly better when powered by a 9V Carbon-Zinc battery.
While modern Alkaline batteries holds more power and lasts longer than Carbon-Zinc 9V batteries, Carbon-Zinc batteries makes guitar pedals in general and Fuzz pedals in particular sound their very best.
Eric Johnson can tell which kind of battery is in his pedals from how they sound, and Analogman has been quoted to prefer Pansonic's Carbon-Zinc batteries for fuzz pedals.
Analogman has an A-B-test posted on his website to showcase the difference in sound between a modern Alkaline battery (Duracell) and a cheap general purpose type Carbon-Zinc battery. The test was made with a Les paul into an Analogman Sunface NKT275, first with the Duracell (twice), then the cheap general purpose type Carbon-Zinc battery and then the Duracell again. Listen to the change in the high-end. The test can be found here :