How to charge a car battery

If you’re wondering how to charge a car battery at home, you may be pleased to know that it’s easier than you think. All you need is the right tools and a little technical and safety know-how. Read on for our simple step-by-step guide that will get you back on the road in no time.

Remember, if your battery gives you trouble while you’re out and about and you don’t have access to a charger or jumper cables, contact your insurer. They may offer breakdown services to help you.

A quick intro: How car batteries work

To start your car, the battery provides a large jolt of amps (a measure of electrical current) to turn over the starter motor and get the car running. The resultant mechanical energy is converted to electrical energy by your car’s alternator, recharging the battery as you drive.

This cycle powers your car and all its electrical components, including the lights, air con, radio, and other essential safety features like ABS and airbags.

Common causes of a flat car battery

A dead car battery can be the result of a few factors, including:

• Most often, a dead battery is the result of its age. In general you can expect a car battery to last between three to five years depending on how often your car is used, its operating climate, and how well it’s maintained. While certain batteries may last as long as seven years, some specialists recommend having your battery tested twice a year after its second birthday.
• Leaving the lights, radio, or other electrical accessories on when the car engine is off can drain the battery. When your car is running, the alternator keeps the battery charged and all its electrical components going. If your battery dies and it’s not an obvious case of the headlights being left on, it may be that some other electrical feature hasn’t turned off automatically when the car does. This causes what is known as a parasitic draw, and will likely need a professional to assess and repair.
• Corroded battery terminals can interrupt your car’s electrical circuit, meaning that it cannot recharge or distribute power correctly. Battery corrosion can appear on the battery posts, terminals and cables and looks like a greenish-blue white powder. It’s caused by hydrogen gas being released by the acid in the battery. It is easily cleaned with either a solution of bicarbonate of soda and water, or a dedicated battery terminal cleaner. Consult your manual to find out how to disconnect your battery before you start the process and importantly wear protective gear such as gloves and goggles when you do. The corrosion residue is caustic and can burn your skin and eyes.
• Your battery works hand in hand with your alternator. A faulty alternator won’t charge your battery, meaning that once all the power stored in your car’s battery is used up you’ll be left with a flat battery and needing a charge. If your car suddenly powers down while on a journey, you’re likely dealing with an alternator issue and will need an auto electrician to diagnose and repair/replace the alternator.

Using a battery charger: A step-by-step guide

In considering the correct way to charge a car battery, it’s always a good idea to go over any directions listed on your battery charger and in your car’s owners manual.

Also make sure that the battery charger you have is compatible with the battery in your car. For example a car with start/stop technology will have an AGM or EFB battery and will require a “smart” charger. If you’re unsure, a quick call to your mechanic can help set you right.

Getting ready

Follow these steps as you prepare to charge your battery:

• Battery chargers can be bought through most auto parts stores and even through some online retailers.
• Charging your car’s battery is best done in a well ventilated area to allow the hydrogen gas generated by the battery to dissipate as you work.
• Depending on the make and model of your car, you may have to remove the battery from its holding tray to charge it, while other batteries can stay right where they are.
• Once your battery is ready to charge, ensure that all your car’s electronics are off.
• Then, detach the negative or ground cable from your car’s battery. It’s usually black and marked with a “-” symbol. In some cars, there may be plastic caps over the terminals that you need to remove before you can access the cables. The terminals are often connected to the battery by clamps. You can usually loosen or tighten these clamps with either a spanner or screwdriver.
• Follow this by removing the positive cable, which is usually red and marked with a “+” symbol.
• You may want to take this opportunity to clean your battery terminals (see above).

When removing the positive and negative cables, it’s important for your safety that they’re placed far away from one another, so that they can’t pass electrical charge between them.

Connecting the charger

Be sure to read and follow the instructions that accompany your charger. In many cases, the steps will look something like this:

1. Make sure the charger is powered off.
2. Connect the positive charger cable to the positive terminal on your car’s battery.
3. Connect the negative charger cable to (in most cases) an unpainted metal part of the engine block to provide grounding, and prevent arcing and a possible explosion. This is often the recommendation when the car’s battery is charged in situ. If the battery has been removed from the vehicle, you may be instructed to use the negative terminal on your car’s battery. Consult your charging manual to determine what’s safest for your car. Take note, it is essential that the positive connection is made first.
4. Once the connection has been correctly set up, turn on your battery charger.
5. Although a higher amperage setting usually means a faster charging time, it’s a good idea to make use of the lowest charging setting (see why below).
6. You can expect the charging process to take several hours. Using the charger’s built-in timer or setting an alarm on your phone, charge your battery for as long as your manual recommends.
7. Once charging is complete, be sure to turn off the charger, and remove the negative cable first, either from the terminal or the metal grounding part of the car. Follow this by disconnecting the positive cable.
8. You can then reattach your car’s cables to its battery terminal, beginning with the positive cable and following with the negative cable. This order is important and can cause you a nasty shock if reversed. Remember to attach the cables securely, tightening any nuts and bolts, and replacing the battery into its tray and clamping in place.

Can you overcharge a car battery?

When using chargers to recharge your car battery, beware of overcharging. This can overheat and damage the battery, reducing its capacity and shortening its lifespan. It’s always recommended to use the lowest amperage setting possible when using an external charger.

Can you charge a car battery while driving?

Because of how the alternator and battery work together, driving your car should recharge the battery. For example, if you have a flat battery and make use of a jump start to get going, a good long drive thereafter should see your battery recharged and easy to start. This will of course depend on the cause of the flat battery in the first place.

Jump starting

To do this you’ll need access to jumper leads and a car with a fully charged battery (let’s call this car A). The car with the flat battery we will call car B.

1. Park the cars in such a way that their batteries are within reach of one another. The cars should not actually touch however and their emergency brakes should be on and the ignitions off.
2. Cable order is paramount. Begin with RED to DEAD. Attach the one end of the red jumper cable to car B’s positive terminal, often red and marked with a “+” symbol, and the other end to car A’s positive terminal.
3. Attach the one end of the black jumper cable to car A’s negative terminal, often black and marked with a “-” symbol. Then take the other end to an earthing point on car B. An unpainted metal part of your car like a bolt or bracket well away from the flat battery and fuel system is best.
4. Allow the cars to remain like this, engines off for three minutes.
5. Turn car A on and allow it to run for a minute or two.
6. Turn on car B’s engine, leaving both cars running for about 10 minutes.
7. Turn both the cars off and disconnect the leads in reverse order, i.e. start with the black lead from car B first and so on.
8. Restart car B.

How long does it take to charge a car battery?

If you’re wondering how long a car takes to charge a dead battery, the time taken will depend on the method of charging.

If you’re using a charger, depending on the car battery model, its age, and the type of charger you’re using, you can expect it to take between 10 to 24 hours to fully recharge.

On the other hand, if you’ve jumpstarted your car, the AA recommends a drive of around 30 minutes in flowing traffic to recharge your battery.

Precautions to take note of when charging your battery

Whichever approach you choose, always remember the following safety measures:

• Cable order is important.
• Keep the charger as far away from the battery as possible.
• Metal objects such as tools or jewellery, and stray wires touching the battery, could cause a dangerous spark. Do not allow any naked flames near the battery either.
• Remember that, in disconnecting your battery, you will likely erase your dashboard settings and other electronics, and newer cars may need the relevant security codes to reset them.
• It’s best not to use a hybrid or electric car when jumpstarting your car. Also ensure that both cars have the same voltage. If in doubt, check your manual.
• Make sure the jumper cables are in good condition and if they begin to get hot, stop using them immediately
• Don’t detach the jumper cables while the cars are running, this could damage the car’s electronics.

Key takeaways

With the right tools and our step-by-step guide, it’s easy to charge your car battery at home and get back on the road.

But if life throws you a curve ball and you find yourself stranded, remember that Howden works with AXA Assistance and RAC Breakdown, ensuring both roadside assistance and vehicle repairs at home for our clients. Contact us today to ensure you’re properly protected.

Also read:

• How often should you service your car?
• A guide to electric car tax
• Are you prepared for extreme weather?
• CAR INSURANCE GUIDES