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Batteries

Energy and power · level 1, lesson 4 of 6

A question to start

A torch works in the middle of a field, far from any plug. A phone works on a bus. Where does their energy come from, and why does it run out?

The idea

A battery is a store of energy. Inside it are chemicals that hold energy until you need it. Connect the battery to a torch, a toy or a phone, and the energy flows out as electricity.

When the energy is used up, the battery is flat. Some batteries are thrown away (and should be recycled); others, like a phone's, are rechargeable: plug them in, and electricity fills them up again.

full: it shinesflat: it doesn't

Batteries are useful because they let us carry energy around, and keep energy for later. A solar panel only works in daylight, but a battery charged during the day can keep the lights on at night.

On Mars, every rover and lander has batteries. The helicopter Ingenuity charged its batteries from a small solar panel each day, then spent much of that energy in a flight lasting a minute or two. Rovers keep their batteries warm at night, because cold batteries work badly.

Worked examples

1. A remote control. It has two small batteries. They slowly run down over months of use.

2. A phone. Its battery fills up overnight from the plug, and empties during the day.

3. A solar garden light. Its panel charges a battery in the day, and the battery lights the lamp at night.

Try it

  1. What does a battery store?
  2. What does "a flat battery" mean?
  3. Why does a solar-powered home on Mars need batteries?
  4. Why do rovers keep their batteries warm?
Answers
  1. Energy.
  2. Its stored energy is used up.
  3. To keep things working at night and when dust blocks the Sun.
  4. Cold batteries work badly, and can be damaged.

Common mistake

"A battery is full of electricity." It is full of chemicals that hold energy. The electricity is made only when the battery is connected in a circuit.

Where it leads