Here's another way to make the battery if you don't have access to zinc washers;
Pick out 10 pennies newer than 1982, and use 100-grit sandpaper to sand one face of the penny. The entire inside of the penny is zinc, so sand the face until the whole surface exposes the zinc.
Once again, cardboard needs to be cut and soaked in an electrolyte like vinegar, salt water, or lemon juice. In this case, I didn't round the edges. You can see the sharp corners, and that's ok as long as they don't touch. If the cardboard pieces touch, that section of the battery will short out and decrease the performance of the unit as a whole.
You can build your battery cells the same way you did with the washers, as long as the pennies are all facing the same direction. With this method, the zinc top is the positive, and the copper bottom is negative.
By connecting 10 cells in series (stacking them on top of each other), the electrical potential will jump to nearly 6 volts! This should be more than enough voltage to drive an LED… or TWO?!?
You can get an LED to light up by pressing the long lead of the LED (positive) on the top, and the short lead of the LED (negative) on the aluminum foil base.
LEGALITIES: Some people have asked about the legality of treating pennies in this manner. The federal law states that there are exceptions made for use as "educational, amusement, novelty, jewelry, and similar purposes as long as the volumes treated and the nature of the treatment make it clear that such treatment is not intended as a means by which to profit solely from the value of the metal content of the coins." For more information, click here