E 6.5 Batteries and Electrolysis.

Zinc-copper-acid battery. Cut-away dry cell Batteries in series and parallel can be demonstrated.
Lemon cell - a copper and zinc nail pushed into a lemon will produce about 0.9 V on a meter. Two lemon cells hooked in series will light a small red led. Bring your own lemons.
Electrolysis of water apparatus is shown in the video below. NaOH is used as the electrolyte. The gasses are tested in the second video. Oxygen will relight a smoldering wood splint. Hydrogen causes a small pop when ignited.