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Car Battery Essentials – D, E and F

Written on March 16, 2016 at 2:31 pm

In this article, we continue our A-Z of car batteries with a look at the next three letters of the alphabet.


D is for Direct Current

A car battery, unlike a household power supply, provides direct current or DC. This means that whilst household electricity known as alternating current (AC) provides electric in the form of a wave, the power output from a car battery appears much closer to a straight line.

Essentially, in a direct current power source, the electrons flow in a single direction.

As well as producing direct current, a car battery requires direct current to charge, which is why all AC power is instantly transformed to DC when a battery is a main part of a system, as occurs in an automotive application, such as motorcycles, cars and trucks. The alternator (also known as dynamo) present in vehicles generates AC current which is instantly transformed to DC through a device called a “rectifier”, because a battery is present and most electronics need DC voltage to operate.

Domestic and commercial battery chargers, as well as quick start devices are typically supplied by AC power and feature circuitry to convert this to DC.


Direct Current

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E is for Electrolyte

An electrolyte is defined as a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. In an automotive battery, the electrolyte is essential to how it works.

In a traditional lead acid battery, each cell contains two plates – one made of lead and the other made of lead dioxide. These plates are immersed in a strong sulphuric acid electrolyte solution. When the battery is in use, lead combines with SO4 (sulfate) to create PbSO4 (lead sulfate), plus one electron.

Lead dioxide, hydrogen ions and SO4 ions, plus electrons from the lead plate, create PbSO4 and water on the lead dioxide plate.

As the battery discharges, both plates build up PbSO4 and water builds up in the acid. The characteristic voltage is about 2 volts per cell, so by combining six cells you get a 12-volt battery.

With a traditional car battery, it is important to try to maintain a charge of at least 50% in order to prevent excessive formation of water, which will cause the battery to stop charging and eventually fail.

Modern VRLA batteries such as Gel and Agm batteries are slightly different, as the electrolyte is not stored in a liquid form but in the form of a thick gel (Gel) or contained within a fibreglass mesh (AGM). This makes them less vulnerable to leakage and therefore generally safer, as well as reducing the risk of failure in cold conditions as they do not tend to produce water buildup to the same extent as a traditional lead acid battery.

AGM batteries are also more electrically reliable, making them the favourable choice for many modern cars which feature lots of on board electronics.


car battery


F is for Failure

There are several reasons why a car battery can fail. However, with a quality battery and the right level of care and maintenance, the good news is that the majority of failures can be avoided. So what are common causes of battery failure?

Excessive Discharge
As mentioned in the previous section, it is important to maintain a charge level of at least 50% in a traditional battery. This ensures that the electrolyte solution does not undergo a complete transformation that leaves the battery with a high volume of water and no ability to transfer current between the terminals. This water build up can also cause problems in low temperatures as it can freeze.
To help avoid excessive discharge, turn off all nonessential electrical features when starting the car and ensure they are off when the vehicle is not running.

Because a traditional lead acid battery contains the electrolyte in a liquid form, damage to the housing can cause leakage. Not only can this be harmful to both humans and the wider environment, over time it will leave your battery without the essential fluid it needs in order to function and once the electrolyte has fallen to a certain level it will stop working.

Self Discharge
If a battery is unused for a significant period of time, separation will occur inside, making the battery much less likely to transfer current between the terminals when you try to start it again. Also, a gathering of substances in the bottom of the battery can actually cause the terminals to short out, discharging any energy that may remain.

At Manbat, we are experts in automotive batteries. To learn more about the technical specifications of our products along with a wealth of battery related information, visit the technical section of our website. Be sure to also stay up to date with our latest news, where we frequently publish interesting and informative battery related articles.

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