Uh....every twentysomething who's living alone has to figure out what a 9-volt is eventually. Fire alarms, yo. I totally get the whole "grizzled old EE" act, but really?

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.

It's that thing they take out of the smoke detectors in their college apartments...

A 9-volt is the boxy one you put on your tongue to get a little tingle!

I'm 20 and know what an 9 volt is. I have also licked one before.

Now if you said 4.5V flat pack lantern batteries, then yes. I've seen like 1 before, and it was dead.

Let alone experience licking one.

Haha! I'm 28, and my dad and I bonded over, among other things, licking a 9-volt battery.

Are 9-volts not around anymore? I haven't seen one, but I don't use anything they used to be common in like toys and radios.

Many smoke detectors/alarms still use it. In Australia smoke detectors now have to be wired to the house but have a backup battery in case of a power failure.

pedantic but you're off 10+ years. We still needed 9 volts in the 90s.

Some of the low power circuits in older amateur radio books use 9-volts.