Science Experiment: Lemon, Potato & Saltwater Batteries
Great for teaching kids how batteries work — but they will NOT charge a phone. Here's what they really do.
Question 1
The goal
Light a small LED using homemade chemical cells and understand why they can't replace real batteries.
Question 2
Materials
- 4–6 lemons, potatoes or cups of saltwater
- Galvanized (zinc-coated) nails or screws
- Copper coins (pre-1982 US pennies) or copper wire
- Alligator clip leads or wire
- Small red LED
- Multimeter (optional)
Question 3
Substitutes
- Vinegar instead of lemons
- Aluminum foil instead of zinc (weaker)
- Copper pipe pieces instead of coins
Where to find it
| Material | Household | Wilderness | Urban / scavenged |
|---|---|---|---|
| Zinc | Galvanized nails, screws | N/A | Hardware store |
| Copper | Old pennies, wire | N/A | Electrical wire scraps |
Question 4
Step by step
- 1
Push one zinc nail and one copper piece into each lemon about 1 in (2–3 cm) apart, not touching.
- 2
Measure with a multimeter: each cell gives about 0.8–1 V.
- 3
Connect cells in series: copper of cell 1 to zinc of cell 2, and so on. Leave one zinc and one copper free at the ends.
- 4
Four cells give roughly 3–4 V — enough voltage to light an LED.
- 5
Connect the LED's long leg to the free copper end and short leg to the free zinc end. Dim the room — the glow is faint.
- 6
If it doesn't light, flip the LED, check every connection, and add more cells.
- 7
Measure current if you have a meter: usually under 1 mA. A phone needs about 1,000–2,000 mA.
- 8
Discuss with kids: it would take thousands of lemons to charge a phone.
- 9
Throw away the lemons/potatoes afterwards — don't eat them (metal ions).
Saved steps go to My Survival Notebook.
Question 5
The science
Zinc gives up electrons more readily than copper. The acidic juice or saltwater lets ions move between them, so electrons flow through the external wire. Voltage depends on the metals; current depends on electrode size and electrolyte, which are tiny here.
Question 6
Dangers & limits
- Don't eat the produce after.
- Never try this with car battery acid or strong chemicals.
- Supervise young children with nails and sharp wires.
Question 7
How you know it worked
The LED glows dimly and you can explain why it isn't practical emergency power.