How to charge a car battery in 3 steps

How to Charge a Car Battery

Car batteries stay charged by using the extra energy from the car’s engine, and most last at least five years without needing to be replaced or recharged. But even the best car batteries eventually run out — or lose their charge prematurely if you leave the lights on too long. Finding yourself with a dead battery can be a serious inconvenience. But recharging one can require very little in terms of tools or mechanical experience.

Preparations for charging the battery

Put on appropriate protective equipment.

Safety always comes first when working on your vehicle. Start by putting on safety goggles to protect yourself from falling material under the hood, sparks, or battery fluid in case the battery becomes damaged. Also, you should wear gloves. Make sure the area you’re working in is well ventilated and has enough lighting so you can see where you’re going and what you’re working on. Gloves are not necessary but can protect your hands from minor bruises and cuts while working on your vehicle. Make sure children are not around while you work on a vehicle battery. Sparks may fly if the positive and negative cables come in contact with each other.

Determine what type of battery you have.

In order to properly charge your battery, you must first determine the type of battery you have. You can usually find this written somewhere on the battery. However, you may need to check the manufacturer’s website if the label is too worn to read or is missing. You should also find out the voltage of the battery by looking at the label or in your vehicle’s owner’s manual. Battery types include: Wet cell batteries are repairable, which means there are things you can do to improve your battery’s charge and lifespan. Valve-regulated lead-acid batteries are completely sealed and require no maintenance. These batteries come in the form of gel cells or absorbed glass mat batteries. They are less common in cars unless they are retrofitted and fitted.

Get a car battery charger.

Find a charger that is right for your battery and purpose. Most chargers are suitable for all types of batteries except gel cell batteries. There are quick chargers that can charge your battery quickly or even jump-start you. However, there are also “drip” chargers that provide a slow but longer-lasting charge. Many newer chargers contain a microprocessor that shows how far the battery has charged. These digital chargers will automatically stop the process when the battery is fully charged. Older, simpler chargers must be switched off manually to prevent dangerous overcharging. They should not be left alone for long periods of time while attached. Read the charger’s user guide to ensure you are using your specific device correctly. Even new digital chargers should be watched closely while they charge. This will ensure they are working properly and shutting down before they overcharge the battery.

Disconnect the connectors and, if necessary, remove the battery from your vehicle.

It is important to disconnect the battery before attempting any repairs or maintenance on your vehicle. Most of the time you can charge the battery without taking it out of the car. However, sometimes it is difficult to reach the battery or to store the charging cables in the engine compartment or trunk where the battery is located. Then remove them completely from the car when you charge them. Check your vehicle’s owner’s manual if you’re not sure where your battery is located. Some vehicles have the battery in the trunk, while most have it under the hood. Disconnect the negative terminal first and then the positive terminal when removing a battery.

Clean the battery poles.

Dirt and grease on the battery posts can prevent a good connection between the cables and the battery. It is therefore important to thoroughly clean the poles. Wipe away any grease or rust with baking soda and a wet cloth or sandpaper. Make sure the metal of the pins is bare before proceeding to the next step to ensure a strong charge. Sometimes you may find that the battery has a solid charge but dirty terminals have prevented the current from flowing. Do not touch the poles with bare hands, especially if there is any white powder on them. This powder is usually dried sulfuric acid, and it can burn your skin if you come in contact with it.

With a speed or trickle charger

Place your charger on a stable surface.

Never place the battery charger directly on top of the battery. It could connect the minus and plus poles together, i.e. cause a short circuit. This will damage the battery and charger and could even cause a fire. Instead, place the charger on a stable surface as far away from the battery as the cables will allow. If you are indoors, make sure the area is well ventilated by opening your garage door or window before plugging the charger into the outlet. Make sure the surface you place your charger on is stable and immobile to prevent it from falling or becoming disconnected from the battery. Use the full length of the cables to keep the battery and charger as far apart as you can.

Connect the charger to the battery.

Connect the charger’s black cable with the minus (-) symbol on it to the battery’s negative post with the same symbol. Then connect the red wire with the plus sign (+) to the positive terminal of the battery with the corresponding symbol. Be sure to check the connections before plugging in or turning on the charger. Reversing the positive and negative terminals could damage the battery or even cause a fire. On some cars, the poles may be labeled with the letters POS instead of a plus sign (+) and NEG instead of a minus sign (-). Make sure the cables are securely attached to allow current to flow from the charger to the battery.

Set the charger.

Digital chargers may display the existing voltage in the battery and let you set the voltage to achieve. Older models, on the other hand, may only allow switching on or off. Fast chargers also let you choose the pace at which you want to charge the battery (often depicted as a turtle for slow charging and a bunny for fast charging). A quick charge is good for a car battery that has recently died (because you left your lights on, or something with the same effect). Conversely, a battery that has been dead for a period of time may require a slower charging method before it can be used again. If you can set the voltage at which the charger stops, set it to the voltage specified on the battery or in the vehicle’s owner’s manual. Never set the charger to fast charge if you leave the vehicle unattended. You may want to charge the battery slowly overnight to fully charge it if it has been empty for some time.

Check the battery.

Check the battery after you charge it to make sure it’s working. Some digital chargers offer an indicator that tells you if the battery is holding the charge properly or if it needs to be replaced. This is often indicated by a percentage such as “100%” when the battery is 100% charged. You may also want to check the battery’s voltage with a voltmeter after you’ve disconnected it from the charger. To do this, touch the positive and negative terminals of the battery with the corresponding leads of the voltmeter. If the battery is still in the car, the easiest way to check it is to simply reconnect it and try to start the car. If the voltmeter reads the correct voltage for the battery, the charger says it’s good, or the vehicle starts, the battery is sufficiently charged. If the voltmeter or charger shows that the battery is bad, or if the vehicle will not start, there may be other issues to resolve or the battery may need to be replaced.

Jump start your battery

Park a working car so that it faces the car you are jump-starting.

Jump starting a vehicle involves using the electrical system of another, running vehicle to charge the battery in yours enough for it to start and charge itself. Before parking the working car, be sure to locate the batteries in both vehicles as they are sometimes located in the trunk. Once you have located both batteries, drive the running vehicle close enough to yours that your jumper cables can be connected to both batteries. If one vehicle’s battery is in the trunk, place it rear-to-back so the cables reach. Put the handbrakes on both vehicles to make sure they don’t move while charging.

Connect the two batteries with the jumper cable.

Remember that touching the plus and minus ends on the leads when the jumper leads are connected to the battery creates dangerous sparks. With both cars off, connect the jumper cable to the positive terminal of the dead battery and then to the positive terminal of the good battery. Be careful not to let the negative cable dangle into the engine compartment. There it could touch metal, which could serve as a ground to complete the circuit. Next, connect the negative cable to the dead battery’s negative terminal, followed by the negative cable to the corresponding terminal of the good one. You may need to clean the terminals on both batteries to ensure a good connection. Be sure to connect the positive sides to the positive poles and the negative cables to the negative poles. Mixing them up could cause damage or a fire.

Start the working car.

Start the working vehicle when the cables are securely connected. This allows the electrical system to start charging the dead battery. Keep the working vehicle idle while charging. Allow the vehicle to run for a few minutes before attempting to start the other vehicle. After a minute or two, try to start the car with the dead battery. If the battery just recently died, it should start immediately. If it doesn’t start after a minute or two, let it charge a little longer. If the battery has been dead for some time, it may take longer to charge sufficiently to start.

Disconnect the cables and let the vehicle run.

When the vehicle starts, you can disconnect the jumper cables from both vehicles. Let the vehicle run a little longer with the previously empty battery. You may have charged the battery enough to start the vehicle. However, if you turn it off right away, there may not be enough power to restart it. By leaving it running, you give the vehicle’s alternator a chance to finish charging the battery. If the vehicle dies again after being disconnected from the other car, make sure the battery is connected securely. If the vehicle is running well, take it for a short drive to give the battery a good charge before turning it off again.

Solve battery problems

Have the battery checked at an auto parts store.

Have you charged the battery with a charger or another vehicle, but it still won’t start? Then remove the battery (if you haven’t already) and take it to an auto parts store. There you can charge the battery and check whether it is working properly, can be serviced or needs to be replaced. If your vehicle’s battery is a valve-regulated lead-acid battery or a wet cell maintenance-free battery, you will need to replace it if it fails to hold a charge. If the battery is defective, you will need to purchase a replacement for it. Is the battery fully charged and working well, but your car still won’t start? Check the battery cables to make sure they are not broken and are securely connected to the battery.

Check the alternator.

A faulty alternator can prevent your vehicle from charging the battery enough to restart the car. It may even produce too little electricity to keep the car running. You can check if you have an alternator problem by starting the vehicle and then disconnecting the positive battery terminal. A properly working alternator produces enough current to run the vehicle without a battery. However, if the vehicle dies, the alternator will likely need to be replaced. Sometimes you can tell if there is a problem with your alternator by looking at the interior lights. If the lights get brighter when you step on the gas pedal and get dimmer when you put your foot down, the alternator may be bad. If you take the alternator out of your vehicle, many auto parts stores can test it to make sure it’s the problem before ordering a replacement.

Listen for a click.

If your car won’t start but makes an audible click when you try, there probably isn’t enough power in the battery to start the vehicle. This could be because it hasn’t been charged properly or is simply too worn out to hold a charge. Attempt to jump-start the car again or remove the battery and have it tested. Make sure you have a good connection with the battery when you charge it, otherwise it won’t be able to start the car. The clicking indicates there is some power in the battery, but not enough to start the engine.

Note if the vehicle stalls.

If the vehicle starts after you charge the battery but stalls soon after it starts running, the alternator could be the problem. However, if it restarts or continues to crank but not run, the problem is not electrical. You could have an air or fuel supply problem. Your vehicle needs air, fuel, and electricity to run properly. You will likely need to take the car to the shop to identify the problem if this happens.



Frank Reid

Frank Reid is Usevoucher Contributing Writer. He covers a wide range of topics, including financial planning, car reviews, travel, entertainment, and lifestyle. He has an extensive journalistic background, where he's written and reported for several newspapers and magazines. Frank lives in New York, and is a native of Texas.