During lectures on electrochemistry, when one discusses standard electrode potentials, some students recognize that the highest voltage battery that can be made is a lithium-fluorine cell (a little over 5 V). The question can come up as to how a 9 V transistor battery is possible. (You may want to pose the rhetorical question yourself.)

The solution to the mystery of the 9 V battery can be shown by opening up such a cell on an overhead projector for all to see. What is inside? Six little 1.5 V batteries!