Things You'll Need
Dissolve salt into water. Mix salt in room temperature or warmer water until no more will dissolve.
Cut out 20 paper pieces that are slightly bigger than a penny. You can use cardboard, plain paper or paper towel. The only thing that matters is that they are a little bigger than the pennies you are using.
Cut 20 pieces of aluminum foil out, measuring each to about the size of a penny. Don't worry about making them exactly the same size.
Make your first battery cell. Pick up a piece of paper with the tweezers and soak it underwater for several seconds. Then carefully place it on top of a penny so that it covers the whole surface. Finally, put a piece of aluminum foil on top of the paper, using the tweezers to center it.
more stacks on top of each other. Stack in the order: penny, paper, foil, penny, paper, foil and so forth. Keep going until you have gone through 20 pennies. You should have a penny on the very bottom and a piece of foil on the very top.
Secure your battery. Carefully wrap it up with plastic wrap to hold it all together. You can get by without doing this step, but it is helpful, since it stops the battery from falling apart. Do not wrap the ends of the battery, since those are your terminals.
Take a Christmas light, electric buzzer, small motor or other little electric gizmo and attach it to the battery. Connect one terminal to the penny on the bottom and the other to the piece of foil on the top. It should shine, buzz or whir, depending on what you are using.