You can make a working battery at home using two different metals and an acidic or salty liquid. The simplest version requires nothing more than a lemon, a copper penny, and a strip of aluminum foil. These DIY batteries produce real electricity, typically around 1 volt per cell, though the current is very small. With a few cells wired together, you can light up an LED.
Every battery, from a tiny coin cell to a car battery, works on the same principle. Understanding that principle will help you build one that actually works.
How Any Battery Works
A battery has three essential parts: two electrodes made of different materials (called the anode and cathode) and a chemical substance between them called an electrolyte. The electrolyte can be a liquid, a paste, or a gel. In a DIY battery, it’s usually an acidic juice or saltwater.
When the two metals sit in the electrolyte, one of them gives up electrons more easily than the other. That difference in reactivity creates a voltage. Connect a wire between the two metals, and electrons flow through it from the more reactive metal to the less reactive one. That flow of electrons is electrical current. Meanwhile, charged atoms (ions) move through the electrolyte to keep the reaction balanced. The whole process is a chemical reaction converting stored chemical energy into electrical energy.
In a lemon battery, for example, aluminum gives up electrons far more readily than copper. That difference drives the current. The lemon juice acts as the electrolyte, allowing ions to travel between the two metals inside the fruit.
Lemon Battery: The Simplest Build
This is the classic beginner project. You’ll need a fresh lemon, a copper penny, a strip of aluminum foil, and a couple of plastic-coated paper clips.
Start by washing the penny with soapy water to remove any grime. Cut a rectangle of aluminum foil about 3 cm by 20 cm, then fold it lengthwise into thirds so you have a sturdy strip roughly 1 cm wide. Roll the lemon on a table with some pressure to loosen the juice inside.
Lay the lemon on its side and make two small parallel cuts near the middle, each about 2 cm long and 1 cm deep, spaced about 1 cm apart. Push the penny into one cut until it’s halfway inside the lemon. Slide the aluminum strip into the other cut. Both metals need to be in contact with the lemon juice inside, because that juice is your electrolyte.
That’s it. You have a single-cell battery. If you touch the free ends of the penny and the aluminum strip to a sensitive voltmeter, you’ll see a reading. A single lemon cell produces real voltage, but very little current. As Battery University notes, any electrical load causes the voltage to collapse almost immediately. To do anything useful, you need to connect multiple cells together.
To chain two lemon batteries, use a second aluminum strip and paper clip to connect the penny of the first lemon to the aluminum electrode of the second. Each additional cell adds its voltage to the total.
Penny Battery: A Stackable Design
This project from the Exploratorium uses pennies themselves as both electrodes, stacked into a neat column that can light an LED.
You’ll need five or more post-1982 U.S. pennies (these have a zinc core with copper plating), a piece of 100-grit sandpaper, thick cardboard or matboard, table salt, vinegar, water, a red LED, and electrical tape.
Preparing the Materials
Make a saturated salt solution by stirring salt into water until no more dissolves, then add a splash of vinegar. Cut the cardboard into small squares roughly the size of a penny, and soak them in the solution until thoroughly wet. Set them on a paper towel so they’re damp but not dripping.
Take four of the five pennies and sand one face of each until the copper plating is completely removed and you see shiny silver-colored zinc underneath. Leave the fifth penny untouched.
Building the Stack
Place one sanded penny zinc-side up (copper side down). Put a damp cardboard square on top. Stack the next sanded penny on that, again zinc-side up, then another damp square. Keep alternating. Place the unsanded penny on the very top, copper side up. The bottom of the stack should also be copper facing down.
The key rule: no two pennies should touch each other directly, and no two cardboard squares should touch each other. Each penny-cardboard pair forms one cell. The saltwater-soaked cardboard is the electrolyte, the zinc face is one electrode, and the copper face of the penny above or below is the other.
Wrap the stack gently with electrical tape to hold it together. Touch the LED’s longer leg (positive lead) to the copper top of the stack and the shorter leg to the zinc bottom. A red LED needs the least voltage to light up, so it’s the easiest to power. If it doesn’t light, try adding another penny-and-cardboard layer to increase the total voltage.
Saltwater Pentacell: Lighting an LED Reliably
If you want a more robust DIY battery, the Exploratorium’s saltwater pentacell uses five separate cups wired together. Each cup holds a copper wire electrode and an aluminum foil electrode sitting in saltwater.
Mix about 2 tablespoons of table salt into 1 quart of water and stir until dissolved. Pour some into five small cups. In each cup, place a strip of copper wire and a separate piece of aluminum foil, making sure they don’t touch each other inside the liquid.
Connect the cells in series: run a wire from the copper electrode of one cup to the aluminum electrode of the next. After linking all five cups, touch the LED leads to the free copper electrode of the first cup and the free aluminum electrode of the last. Five cells in series reliably produce enough voltage to light a red LED. If it still won’t glow, adding half a teaspoon of vinegar to each cup can improve conductivity.
Aluminum is the more active metal here, giving up electrons more easily than copper. That reactivity difference is what drives the current. You can experiment with other electrode metals: galvanized nails (zinc coated), iron nails, brass hardware, or even carbon pencil lead as a non-metallic electrode.
Why DIY Batteries Produce So Little Power
A copper-zinc cell generates a theoretical voltage of about 1.1 volts, which is comparable to a single commercial AA cell (1.5 volts). But voltage is only half the story. Current, measured in milliamps, determines whether your battery can actually do work. DIY batteries have high internal resistance because their electrolytes are weak and their electrode surface areas are small. That’s why a lemon battery might register 0.9 volts on a meter but can barely make an LED flicker.
You can improve output by increasing the surface area of your electrodes (use larger metal pieces), using a stronger electrolyte (more salt, more acid), or reducing the distance between the two electrodes inside the liquid.
Wiring Cells for More Voltage or More Current
Once you’ve built individual cells, how you connect them determines what your battery bank can do.
- Series (more voltage): Connect the positive electrode of one cell to the negative electrode of the next. Each cell’s voltage adds together. Three cells at 1 volt each give you 3 volts total. Current capacity stays the same as a single cell.
- Parallel (more current): Connect all positive electrodes together and all negative electrodes together. Voltage stays the same as one cell, but the total current capacity multiplies by the number of cells.
- Series-parallel (both): Wire a few cells in series to get the voltage you need, then connect multiple series strings in parallel to increase current. This is how large battery banks are built.
For most DIY projects, series wiring is what you want. A single cell won’t light an LED because the voltage is too low. Five or six cells in series will cross the threshold for a red LED, which needs the least voltage of any color. Blue and white LEDs require more voltage, so you’d need additional cells.
A Note on the Original Battery
Every one of these projects is a variation of the voltaic pile, invented by Alessandro Volta in 1800. His design used alternating discs of zinc and copper, each about 7 cm across, separated by pads soaked in saltwater. The stack produced a steady voltage and was the first device to deliver continuous electrical current. The penny battery is essentially a miniature voltaic pile. Two centuries later, the chemistry hasn’t changed.