Skip the tangled strings of holiday lights this year and go wireless using a few copper-coated cents. U.S. pennies minted since 1982 conceal a zinc core. If exposed to acid, the zinc dissolves and frees electrons for use in a circuit. The battery will run until the liquid dries up or the chemical reaction dies. DIY enthusiast Grant Thompson recently made a 10-penny battery that powered a small light for nearly two weeks. See how far you can stretch your money.
Time: 20 minutes
Cost: About $5
Difficulty: 1 out of 5
1. 1 lemon
2. One 3mm LED
3. 150-grit aluminum oxide sandpaper
4. Electrical tape
5. Duct tape
6. 5 to 10 pennies
1. Fold a piece of duct tape into a sticky square, attach it to a table, and affix a penny. Sand one side until the zinc is fully exposed. Repeat for all but one penny.
2. Cut discs of cardboard—one for each penny—slightly smaller than the coin. Soak the cardboard in fresh lemon juice (vinegar is less acidic but works).
3. Lay a sanded penny copper side down on a table and add a damp cardboard disc on top. Repeat until you have a stack of at least five pennies and four discs.
4. End the stack with the intact penny. Wind electrical tape around the cylinder; the more airtight the seal, the longer the battery will last.
5. Tape the LED’s short end to the intact penny (negative terminal) and its long end to the sanded penny (positive terminal). The LED should light up.
6. Repeat steps 1 through 5 for additional self-powered holiday cheer.
_This article originally appeared in the December 2013 issue of _Popular Science.