Stored energy

Saltwater battery

Copper and aluminium strips in salt water light an LED.

₹5030 minutesEasy

Jump to the steps
CopperAluminiumSalt water

The big idea

A battery needs two different metals and a liquid that carries charge. Salt water is a good liquid for it.

You will need

Tick things off as you gather them.

Step by step

  1. Make the salt water

    Fill each cup with warm water and stir in 3 spoons of salt until it has dissolved.

  2. Add the metals

    In each cup, put one copper strip and one aluminium strip on opposite sides, not touching, with the tops resting on the rim.

  3. Join the cups in a chain

    Connect the copper in cup 1 to the aluminium in cup 2. Then copper in cup 2 to aluminium in cup 3. Carry on to the end.

  4. Add the LED

    Connect the free copper at one end of the chain to the long leg of the LED. Connect the free aluminium at the other end to the short leg.

  5. Watch the LED

    The LED should glow dimly. If not, add another cup, or check that the metals are clean and the clips make good contact.

  6. Measure the voltage

    If you have a multimeter, measure one cup, then two, then three. Note how each cup adds to the total.

  7. Try changing it

    Try more salt, warmer water, or larger strips. Which change makes the biggest difference?

What to look for

  • One cup is not enough. A chain of three or four can light an LED.
  • Tiny bubbles form on the metals.
  • The aluminium slowly wears away.

Why it works

Aluminium gives up its electrons more readily than copper. The salt dissolves into charged particles that carry the charge through the water between the two metals. Electrons flow from the aluminium round the wire, through the LED, to the copper, and light it. Each cup adds a little voltage. The energy comes from the aluminium slowly being used up.

Try this next

  • Try a different pair of metals.
  • See how long the LED lasts.
  • Compare with the lemon battery.

Stay safe

Do not drink the salt water. Wash your hands afterwards.

Link to the grid

Big grid batteries work on the same principle, using better chemistry so they can be recharged thousands of times.

Learn how the grid works

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