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How do (rechargeable) batteries work?

While rechargeable batteries were invented over a hundred years ago, their application hasn’t been around for that long. Today, rechargeable batteries are intertwined with our daily lives: portable devices and appliances have become immensely popular. But how do rechargeable batteries work? And what does a charger do? In this article, we’ll explore the basics of (rechargeable) battery functionality.

A bit of chemistry

Like everything, a battery is made up of atoms. One atom is made up of three types of particles:

  • protons (positive)
  • electrons (negative)
  • neutrons

Ideally, that charge is evened out: the amount of negative and positive particles is equal. Removing one electron (i.e. a negative particle) causes the atom to become positive and vice versa. As atoms prefer to stay neutral, they will look for other atoms to trade electrons to restore their balance. That trade or ‘flow’ of electrons creates a current of electricity.

Anode, electrolyte and cathode

The process of trading electrons also occurs in batteries. Every battery is made up of three parts: an anode, electrolyte and a cathode. Different battery types use different chemicals to create these parts, however.

In a full battery, the anode is negative and the cathode is positive. Why? The anode contains an excess of (negative) electrons, whereas the cathode lacks electrons. Naturally, the anode would want to lose some of its electrons by passing the excess electrons to the cathode.

By adding a third element, the separator with electrolyte, you can control the flow and create a battery. The separator acts as a barrier inside the cell between anode and cathode. It only allows an electric current to flow when the battery is connected to a device.

How rechargeable batteries work

All batteries work this way: electrons travel from an anode to a cathode until the anode is out of electrons. Thus, the battery is considered empty or ‘dead’.

With primary batteries, that’s the end of it. With secondary or rechargeable batteries, a charger can reverse the electron flow and as such restore the initial excess of electrons in the anode - thus creating what we call a charged battery.

Whether or not this reaction can be reversed depends on the chemicals used within the battery. Alkaline batteries, for example, aren’t made to allow a reverse flow. Doing so could potentially be dangerous.

A NiMH (Nickel-Metal Hybride) battery allows a forced reverse flow for hundreds, sometimes thousands of times. The process does however cause damage to the chemicals over time. You therefore can’t infinitely recharge and deplete batteries: at some point, the chemicals will have degraded too much to still hold a charge.

Further reading

How do rechargeable batteries work time after time, then? How great the lifespan of a re-chargeable battery is depends on the manufacturer, the type of battery and the conditions in which it is used. To know more about how NiMH batteries are made, please refer to one of our previous articles here.