- 5 or more post-1982 pennies*
- 100-grit sandpaper
- matboard or thick carboard
- water in a small cup
- a red LED. High-intensity ones are better because the light is easier to see. (Radio Shack #276-309 and 276-307 or MUCH cheaper online at Jameco #1555489)
- (optional) electrical tape, voltmeter
*Legal Disclaimer: Before 1982, pennies were made of 95% copper, but the rising costs of copper led the United States Mint to change the composition of the penny. The metal content in a pre-1982 penny is actually worth more than its one-cent face value. Consequently, in December 2006, the United States Mint implemented regulations that prohibit the melting or treatment of all one-cent coins. The Exploratorium does not take responsibility for any damaged coinage, and certainly don’t try to sell your battery for more than 5¢!