Why is the "C" battery in the extra's a 9 volt? C batteries are just like D but slightly smaller.

The graphic which appears @11:32 shows AA, AAA, C, and D cell batteries. However, the C battery shown is actually a 9 volt type, not an actual C cell. Looking at the graphic a second time, the AA battery has a correct width/height ratio of .28. The battery labeled AAA is actually AA since the width/height ratio is .27. In reality the ratio should be .23. The height of an actual AAA is only 1mm less than a 9 volt battery. Yes, I know, I've apparently got too much time on my hands. But in my defense, it just didn't look right and I had to figure out why.

the C battery is actually a 9 volt in your image.

I enjoyed your approach to and presentation of this subject. You packed in a lot of good information and kept it interesting. One small point. In your graphic of battery sizes, you labelled the 9-volt battery as a C-cell. That is incorrect. A C-cell is a cylindrical battery a bit smaller than a D-cell.

The Leyden Jar was not a battery. It was a capacitor.

I love how every time Ben Franklin is brought up, the conversation always ends in pure delight.

B batteries were typically stacks of individual cells, built in to one package. They were used on tube-based devices to provide the high-voltage for negative grid or positive anode voltages.

Your C battery is actually a 9volt.

A lithium-zinc battery would likely be very effective.

Why do you have a 9V battery labelled as "C" ?

Have you heard of the Baghdad Battery?

The Baghdad Battery dates from about 150 BC to 650 AD or so.