Everything you need to know about car batteries
Updated 31 Oct 2019
What does my car’s battery actually do?
Simply put, the battery stores electricity and has a dual role - to give the engine a kickstart of energy and to supply electricity to the vehicle’s accessories when the engine is not running.
Traditionally, this job required that the battery supply a large amount of current, but only for a small period of time.
As vehicles become more complex, come fitted with more power-hungry components (heated seats, phone chargers, infotainment screens, cameras etc) and features such as stop/start technology that require many kickstart boosts in one trip, there is a lot more demand placed on the battery.
Manufacturers have, therefore, developed a range of battery types and technologies that can deliver power over longer periods and survive the discharging and recharging process without loss of performance.
Almost all car batteries are a variation on the lead-acid technology that uses the chemical reaction between lead plates, sulphuric acid and distilled water to create electrical power.
Flooded Cell Battery:
The entry-level and most common type of battery. These can come as low-maintenance batteries (which may require top-ups of distilled water and can be serviced if required) or maintenance-free.
Enhanced Flooded Battery:
Has an improved lifecycle over the standard battery and better-charging acceptance. Can be used for stop/start technology vehicles.
Has calcium added to the internal plates which makes them more robust, delivers a longer lifespan and an increase in available power, and reduces the formation of hydrogen during the chemical reaction process (known as gassing).
Instead of a liquid, the acid in the battery is suspended safely in gel. This makes the battery 100% leakproof and gives them greater resistance to extreme temperatures and shocks.
Absorbent Glass Mat Battery (AGM):
This battery has the most advanced lead-acid technology and is capable of powering the most demanding of vehicles and accessories.
A glass mat between the plates soaks up all the acid and provides very high cyclic stability.
This enables the battery to be repeatedly charged and discharged without any loss of performance.
: Some manufacturers now use lithium-ion batteries in vehicles.
They are lightweight (offering up to an 80% weight reduction on lead-acid competitors), charge quickly, have a long lifespan and excellent deep cycle capabilities - meaning they can be almost completely discharged and then recharged with no real issues.
They are significantly more expensive than other types of batteries and have specialised charging needs and maintenance procedures.
Which battery do I use?
When your vehicle won’t start, it’s very easy to blame the battery.
Often it will be the cause, but there could also be issues with the starter motor and/or the alternator.
It’s important to have any problem properly diagnosed, but if the battery is causing the issue then you’ll likely need a replacement.
However, the installation of the wrong battery can cause huge damage to a modern car’s electrical system.
To get it right, there are two useful places to turn for assistance.
Firstly, there’s your manufacturer’s owner manual.
Car makers design and build their vehicles with precise specifications in mind and the manual details those specifications and should tell you exactly what you need to know.
Secondly, use AutoGuru to book the services of a qualified mechanic.
Your car is an expensive piece of kit, so don’t risk everything by having a go yourself.
If you get it wrong and damage the electrical system, you, and your wallet, could be in for a nasty shock.
Zak has been working in the auto industry for 40 years.
For the past decade, he has been in the education business, training apprentices and preparing them for a career in the light vehicle and auto electrical trades.