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everyday-engineering

How Batteries Work

A battery uses chemistry to push electrons around a complete path.

Imagine two water tanks at different heights. Connect them and water flows toward the lower tank; a battery creates an electrical difference that can push charge through a circuit.

  1. A cutaway battery with two electrodes, electrolyte, and a separator between them.Negative electrodeSeparatorPositive electrodeElectrolyte aroundthem

    Step 1

    A battery has two sides

    Two different electrodes sit in an electrolyte, with a separator keeping them from touching directly.

  2. Many electrons at one battery electrode and fewer at the other, creating voltage.Negative sideMore availableelectronsPositive sideAccepts electrons

    Step 2

    Chemistry creates a voltage

    Reactions make electrons more available at one electrode than the other. This electrical difference is voltage.

  3. Electrons blocked by the separator inside a battery and pointed toward an outer wire.ElectronsBlocked insideUse the wire

    Step 3

    The separator blocks a shortcut

    Electrons cannot cross straight through the separator, so they need an outside path.

  4. A closed circuit connecting both battery terminals through a lamp.AgainNegative terminalWireDevicePositive terminal

    Step 4

    Closing the circuit opens a path

    Connect both terminals through a device and electrons can move through the outer circuit.

  5. Electrons moving through an outer wire while ions move through electrolyte inside the battery.Outside batteryElectrons use thewireDevice receivesenergyInside batteryIons useelectrolyteReactions staybalanced

    Step 5

    Ions move inside

    While electrons travel through the wire, charged atoms called ions move through the electrolyte to keep reactions going.

  6. A charged battery gradually losing available reactants, then a rechargeable battery reversing the process.ChargedWorkingDischargedRecharge

    Step 6

    Reactions eventually run down

    As materials change, the battery can no longer maintain enough voltage. Rechargeable batteries can reverse many of those changes.

Common trap

A battery stores loose electricity like a bucket.

A battery stores chemical energy. Its reactions create voltage that moves charge when a complete circuit is connected.

Quick check

Why do electrons travel through the device instead of straight through the battery?

  1. The separator blocks their direct path
  2. Electrons are afraid of chemicals
  3. The positive terminal has no charge
Show the answer

The separator allows needed ion movement but prevents electrons from taking a direct internal shortcut.

Sources

  1. DOE Explains...BatteriesU.S. Department of Energy
  2. How does a battery work?MIT School of Engineering