How to charge a car battery

A battery warning sign appearing on a vehicles dashboard.

How to charge a car battery correctly is a question we are often asked – unfortunately this is often when attending an assistance call where battery problems have led to a breakdown.

Although most car batteries can provide trouble free motoring for between three to five years when cared for correctly, occasions do arise when recharging will be necessary.

 

Why do car batteries go flat?

There are a number of reasons for a flat car battery, the most common being old age –more than five years for a car battery should be considered a good life cycle. Essentially, a car battery is only used for cranking the car engine when it is initially started. However, over time as it ages, it will experience a natural fall off in its capacity to hold its charge, and will go dead more frequently. There are other reasons for a battery running flat, including;

·        Frequent short journeys do not allow the battery to fully recharge

·        The use of onboard electronic devices when the car is not running

·        Even leaving  an interior light on overnight when the vehicle is not in use could drain a battery

·        Extreme temperatures, both hot and cold

·        Fitting the wrong battery, one that cannot meet the demands of the car

·        Overcharging a battery

How long does it take to charge a car battery?

Battery charging times can vary from make and model, and can differ depending on the batteries amps and charger that you’re using. High speed charging is usually 6-10amps, whereas low speed charging is typically 2-3amps which is usual for a gradual overnight charge.

We recommend that you opt for a slower charge to prevent the risk of the battery plates becoming buckled.

How do you charge a car battery?

Providing the battery is not excessively past its expected life cycle, with the right equipment, charging a car battery is not difficult. From this step by step guide you can confidently charge your car battery both safely and efficiently. Remember you should never charge leaking or damaged car batteries.

First, check the car battery charger you propose to use is suitable for your particular battery. If you have an AGM or EFB battery you will need a smart charger

Clean the lead terminals. If the lead terminal poles of the battery look dirty or corroded, ensure that you clean them with a wire brush and wipe away any residue before charging. With a conventional unsealed battery check the electrolyte levels completely cover the plates as you may need to top up with distilled water. This will extend the batteries life and will reduce any risks of excessive gassing and bubbling

Before disconnecting the battery, as a precautionary measure, ensure you have any PIN codes readily at hand for your electrical components, navigational system, radio, etc, as they may need to be reset when you reconnect it.

It is important to disconnect the negative lead first to prevent electrical shock, and reconnect it last. Loosen the clamps or screws that connect the battery to the terminals and disconnect the securing mechanism that holds the battery in its housing. Use care to avoid spillage when handling and moving the battery to the site of charging.

When the battery is sited on a stable, flat surface ready for charging, connect the battery charger’s cables to the battery by matching positive to positive and negative to negative. When they have been secured, plug the charger into your electric supply. Ensure that the battery and the charger are separated as far away as possible from each other.

Before switching on the electrical power to charge your battery refer to the manual that was supplied with the charger. Check if you need to switch it off manually when the battery is fully charged, or if it will automatically switch off when the charging cycle is complete.

Please refer to our guidance notes on choosing the correct battery charger for your make and model of vehicle.

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