I have six young relatives (nephews and a niece) that are all 19 or younger. I'd bet that all of them but maybe the 2-year-old know what a battery (of this type) is and all but the 2-year-old and maybe the 6-year-old can name different types.

Remember, their phones and tablets charge from a cable but their toys and remote controls use 9-volt, AAA, AA, and D batteries.

Edit: I guess you were emphasizing the obscurity of the 9-volt in particular, but I think they probably have several things that use 9-volts.