Penny Battery

So you probably already knew that you could make a battery out of pennies.  You'll need a bunch of zinc pennies with the zinc exposed on one side (file or sand the copper coating off on one side).  Cut some cardboard or paper towels or other absorbent material into penny sized pieces and then soak them in an acidic solution like vinegar or lemon juice. Once the pieces are saturated, stack the pennies (all zinc side down) with a piece of the saturated material in between each one.  Then touch the wires from an led light to each end, or attach each end to a small calculator or watch.  As long as the cardboard stays wet, the penny battery will work.  Once the pieces dry out, you'll have to saturate them again. You probably couldn't power your cell phone or DS with it unless you had a big old stack of pennies, but it's still a cool little experiment.  Here is a youtube video that explains the process very well.