How Does a Car Battery Work?

Battery problems are the most common reason for breakdown organizations to be called out. This is frequently down to human error, like leaving lights on, but often it is because of preventable faults due to poor maintenance, damage or simple old age.

Please note that we are talking about conventional petrol and diesel engined cars where the battery is primarily a starter battery. Electric powered cars and hybrid power cars use specialist batteries, usually lithium ion, and their use and maintenance is explained in the car’s handbook.

What does it do?

Modern cars use a lot of power even when parked, when the battery powers alarms, information storage systems and comfort items like stereos. A 1960s car consumed about 300 watts of power but even a modest modern one uses more than three times that – and that is without using the starter. The starter needs a terrific amount of power to turn the engine over, especially on a cold day, which is why failure to start is the most major problem resulting from poor battery condition.

A car battery stores power rather than producing it through chemical reaction like an alkaline battery in a torch. The battery is charged by the alternator, a type of generator driven by a belt from the engine. When you switch something on, with the car running, the power is drawn first from the alternator, but if that is unable to produce enough, perhaps because the car is at idle with lots of equipment turned on, power is drawn from the battery. As you drive off and engine speed increases, the alternator is able to produce enough power both to run the devices and charge the battery. That is why short journeys in poor weather can be such a drain on the battery.

Indeed, the battery manufacturer Varta suggests that cars used mainly for short journeys may benefit from having a battery of greater capacity than is usual for the car. This doesn’t mean it produces more than 12 volts but that it can store more power.

When you start the car you are relying purely on stored power because the alternator can’t produce more until the engine is running.

How does it work?

Inside the battery are sets of electrode plates welded together. The positive ones are lead dioxide and the negative ones are sponge lead while ions passing between them are carried by the sulphuric acid, electrolyte. As the battery discharges (gives out electricity) lead sulphate is formed, but when it is recharged by the alternator that is turned back into lead dioxide and sulphuric acid.

Cars made since the 1960s have what is known as a negative earth. This means the negative terminal on the battery is connected to the car’s body. This earths it and means that when components are connected up, the negative connection can be made to the nearest part of the body.

Related posts:

  1. How to Maintain Your Car Battery
  2. How to Replace a Starter – Changing Starter Guide
  3. Homemade Auto Battery Charger
  4. What Causes a Slow Cranking on Your Car
  5. How to Troubleshoot a Car That Won’t Start

Filed Under: Car Parts


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