How Batteries Work

The little energy pack

Think of all the things that work without a plug: torches, remote controls, toy cars, watches and many more. What do they all have inside? A battery! A battery is like a tiny energy pack. It stores energy and then gives it out as electricity to make things work.

But how does a small object like a battery push electricity all the way around a torch? Let's open up the mystery and find out. (If you would like to learn where electricity comes from first, visit electricity basics.)

Energy stored inside

A battery is full of special chemicals. These chemicals hold stored energy, which we call chemical energy. It is a bit like food: your food stores energy that your body can use later. A battery stores energy that a circuit can use later.

When you connect a battery into a circuit, something clever happens. The chemicals inside slowly react and change the chemical energy into electrical energy. That electrical energy is the push that drives the electricity around the loop. So a battery is really an energy changer: chemical energy in, electrical energy out.

The two ends: + and −

Look closely at a battery and you will see two markings: a + sign and a − sign.

• The + end is called the positive end (the one with the little bump on an AA battery).
• The − end is called the negative end (the flat one).

These two ends matter a lot. The electricity flows out of one end, all the way around the circuit, and back in the other end. That is why your toys have a little picture showing which way the battery must go. Put it in backwards and the toy will not work, because the push goes the wrong way!

The battery needs a complete loop

Here is something surprising: a battery sitting on a shelf is not pushing any electricity at all. It only does its job when it is part of a complete circuit — an unbroken loop of wire from one end of the battery, through the bulb or motor, and back to the other end.

• Complete loop → the battery pushes electricity round → the bulb lights. ✅
• Broken loop (a gap or a switch turned off) → no electricity flows → nothing happens. ❌

So a battery and a circuit work together as a team. You can read more about these loops in how electric circuits work.

Why batteries go flat

You may have noticed that batteries do not last forever. After a while, your torch goes dim and then stops. The battery has gone flat.

Why? Because the stored chemicals get used up. Each time the battery pushes electricity, a little of the chemical energy is turned into electrical energy and used. Bit by bit, the store runs down — just like a snack box that slowly empties. When the chemicals are all used up, the battery can no longer push, so it goes flat.

There are two kinds of battery:

• Single-use batteries cannot be filled up again. When they are flat, you recycle them.
• Rechargeable batteries can be filled with energy again using a charger, which reverses the chemical changes. That is how a phone or a rechargeable toy gets ready to use again.

A safety reminder ⚠️

Small batteries like AA and AAA are safe for making circuits, but follow these rules:

• Never join both ends of a battery together with only wire — this is a short circuit and makes the battery hot.
• Never cut open a battery; the chemicals can hurt you.
• Never put small round button batteries in your mouth — they are very dangerous if swallowed.
• Never use electricity from a wall socket or charger plug — mains electricity is extremely dangerous.

Try it yourself! 🧪

Make a fruit battery! This is a real, safe battery you can build from a lemon. Ask an adult to help.

You need: a lemon (or a potato), a copper coin or copper strip, a galvanised (zinc) nail, and a small LED or — even better — a teacher's voltmeter to see the reading.

1. Squeeze and roll the lemon gently on the table to get the juice flowing inside.
2. Push the copper coin into the lemon on one side, and the zinc nail into the lemon a little way apart from it. Do not let them touch.
3. The lemon juice reacts with the two different metals, just like the chemicals in a real battery. This makes a tiny bit of electricity!
4. Touch the voltmeter wires to the coin and the nail — you will see a small voltage. The lemon has become a weak battery.
5. Experiment: try a potato instead, or join two lemons together with wire to make the push bigger.

⚠️ Safety: Do not eat the fruit afterwards, because the metals have been in it. The amount of electricity is tiny and harmless. Never use a wall socket for any experiment.

You have just built your very own battery and seen chemical energy turn into electrical energy — exactly what happens inside every battery that powers your toys and torches!