By Sharon Sweeny, Updated March 24, 2022

PAVEL IARUNICHEV/iStock/GettyImages

Building a simple dry‑cell battery is a hands‑on way to explore how electricity can be generated without hazardous chemicals. All you need is a handful of common coins, a coffee filter, and a little salt water.

Materials

• 5 pennies minted before 1982 (copper core) – must be pre‑1982 for sufficient copper content
• 5 dimes
• Basket‑type coffee filter
• Salt water (1 tablespoon salt per 1 cup warm water)
• 2 alligator clips
• Small square of corrugated cardboard (~2 inches)
• Galvanometer (or a small flashlight bulb as a simple indicator)

Step 1: Prepare the Salt Solution

Mix 1 tablespoon of salt into 1 cup of warm water until fully dissolved.

Step 2: Treat the Filter

Soak the coffee filter in the salt solution. Then gently squeeze out excess liquid and cut the paper into pieces just larger than a penny.

Step 3: Assemble the Stack

Place the filter pieces between the coins in alternating order: penny, dime, penny, dime, ending with a dime on top. Do not place filter paper under the bottom penny or on the top dime.

Step 4: Connect the Circuit

Attach one alligator clip to the bottom penny and to one terminal of the galvanometer. Place a cardboard square under the stack to keep it level and stable. Connect the second alligator clip to the top dime and to the other galvanometer terminal. If you lack a galvanometer, touch both alligator clip ends to the base of a small flashlight bulb to complete the circuit and light the bulb.

Step 5: Observe the Output

Watch the galvanometer needle move as the homemade battery produces a measurable voltage. If using a bulb, notice it glow as current flows.

TL;DR

Only pre‑1982 pennies work because they contain a copper core; newer pennies are copper‑plated and provide insufficient copper to generate electricity.

Safety Note

Ensure that the filter paper separates the pennies from the dimes—direct contact will short the cell and render the experiment ineffective.