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This 9v battery contained six cells stacked like a layer cake
(lemmy.sdf.org)
Picture of a disassembled Duracell 9v battery. Below the terminal assembly is a clear plastic case where you can see six sets of stacked rectangular terminals and fillings.
I had one of those in my bedroom growing up!
A friend of mine had one as a teenager and then brought it with him to his dorm room after high school. We called it Pavlov because it had to be answered when it rang.