This will teach indestructable build a simple electrolytic cell made with citrus fruits and objects found in any home.
Sorry for my English, I'm Brazilian so I do not speak English well.
Step 1: hunt for materials
citrus fruits (in my case I used the lemon Galician, but you can use oranges or even use citrus, opting for some acid like vinegar or sea water)
One or more penny
1 nail or screw (1 nails or screws (or whatever is made of a metal other than the money)
A multimeter or a voltmeter