Step 3: Power a Calculator With 3 Pennies!
Pick up a calculator from the dollar store and remove the screws on the back so you can get to the battery. Remove it, and save it for another project.
Now pull the negative and positive leads out of the casing and attach wires to the terminals if you can. I just twisted the wires to the battery leads, and used electrical tape to hold them together.
Now it's time to make the penny battery.
I found the easiest way to make one is to combine the pennies with some zinc washers from the hardware store. A pack of 30 is about $1.
Get some cardboard, and cut circular pieces so that the edges are just bigger than the pennies. Let them soak in white vinegar for about 1 - 2 minutes.
Note: Any kind of vinegar should work, and if you don't have vinegar, try salt water, or lemon juice. They will all work just fine.
Start your battery cell by placing a piece of aluminum foil on your workspace, and place 1 zinc washer at the end. Next, take a piece of cardboard, soaked in vinegar, blot dry it on some paper towel, and place it on top of the washer. Lastly, place the copper penny on top of the cardboard, and the battery is done!
An individual battery cell is a zinc bottom, copper top, and separated by a material like paper or cardboard that's been soaked in an electrolyte.
From my testing, each cell yields just over 0.6 volts, and around 700mA. The copper top is positive, and the zinc bottom is negative. This calculator needs around 1.5 volts, so I used 3 pennies, 3 washers, and 3 pieces of cardboard soaked in white vinegar. (3 cells x 0.6 volts = 1.8 volts approximately)
I added wires to the top and bottom for ease of use, then used some electrical tape to hold it together. The aluminum foil is no longer needed.
This type of battery cell is pretty much the same as the first one ever invented by Alessandro Volta in the early 1800's, which came to be known as the "voltaic pile".