How Do Batteries Work? Technical Details and Applications

We use batteries in everyday life and many of our devices are reliant on them, but how do batteries work? The main focus of this section is rechargeable batteries as they are fundamental to battery-backup and off-grid home solar arrays. There are many different types of both rechargeable and non-rechargeable batteries, and each requires separate treatment.

Before proceeding to the specifics for each type of battery you may want to refresh yourself with some of the basics.

* What is a metal and why are they used in batteries? Understanding the structure of metals is a precursor to knowing why an electrical current can be extracted from them. Find metal information here.

* What is happening when a metal rusts? Corrosion is the result of transfer of electrons between the metal and another non-metal substance. Here you can find the answer to the question, What Is Rust?

* How can I learn more about the reactions involved? The reactions that take place in a battery are complex but not beyond our understanding. The process of an element losing electrons is called oxidation. An element that gains electrons is said to be undergoing reduction. Together these form a reaction pair called a redox reaction (reduction and oxidation together). We can track the movement of electrons in chemical reactions by using oxidation number rules which gives us insight into how the chemical reactions in batteries generate electron flow. Once we can assign oxidation numbers, have a clear understanding of exactly what oxidation reduction reactions are, and balancing redox reactions, we are ready to look closely at the functioning of different types of batteries.

Redox reactions are fundamental to battery electrical discharge and recharging, and therefore critical to the success of battery backup solar systems.

* How does a battery generate electricity? The controlled corrosion of metals in batteries gives electron flow. The metal corrodes, or is oxidized, and released electrons in the process. Unless a battery has been designed so that reversing this process, ie supplying electricity, will undo the oxidation of the metal the battery will eventually cease to function. This is why batteries eventually go "flat".

The best way to understand this process is to make a battery cell from some readily available household items and see the sacrificial corrosion at work first hand.

* The history of batteries. Once the principle of metal corrosion producing electrical current was identified, battery technology advanced rapidly. The lead acid accumulator batteries we all rely on to start our cars was a very early development and is still in widespread use today.


How do Batteries Work: The Lead Acid Accumulator

These are also the batteries used to back up solar power systems. A large array of these batteries is connected to the solar panel system and kept optimally charged by a charge controller. These batteries provide sufficient stored electricity to power the home through the dark hours.

Lead acid accumulators are also used in many other applications.


The Nickel-Cadmium Battery (Ni-Cad)

These sealed batteries are used in smaller devices than the larger Lead Acid Accumulators. Their main feature is their ability to deliver a steady potential of 1.25 Volts until it is completely exhausted. This makes these cells excellent for use in devices that require constant, steady power.

These batteries are also rechargeable, though the amount of charge they can hold slowly diminishes over time. While a fully charged N-Cad battery does not last as long as the equivalent sized single-use Alkaline cell, their ability to be re-used makes them a sound environmental choice.


How do Batteries Work: The Nickel-Metal Hydride Battery (NiMH)

As with Ni-Cad batteries, these are a regular feature of small electronic devices and are rechargeable. These cells are usually of the AAA or AA size. NiMH batteries are also sometimes found in larger applications such as cars where, obviously, the batteries are scaled up for the purpose.

NiMH batteries can be recharged many hundreds of times. A fully charged NiMH battery offers similar performance to a single use alkaline cell of the same size.