How to Charge a Car Battery

The best ways to reenergize your car’s main battery

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It’s no secret that a car won’t run if it doesn’t have a decent battery under the hood. The battery is the thing that adds the jolt of energy to start the whole combustion process. 

While most people know that a dead battery means it’s time for a replacement, you can actually save yourself some time and money by charging instead. If it can still hold a charge, recharging the battery is the more cost-effective approach with the right equipment. 

Safety

Dealing with a car battery presents some risks you can mitigate if you take a few safety precautions. 

  • Inspect the battery for any signs of damage. Cracks and corrosions can lead to dangerous acid leaks and other issues. 
  • Never connect anything that shouldn’t be connected. Battery terminals and cables all have an appropriate connector for a reason.
  • Never try to recharge a dried-out battery. Some car batteries may need some distilled water above the battery plates to recharge.
  • Clean battery terminals and cables. A clean connection is best for efficient use and charging. 

Things You’ll Need

Here are the tools you’ll need to recharge your battery:

  • Dead Car Battery: This is what you need to charge.
  • Car Battery Charger: The very thing that will do the battery charging.
  • Safety Wear: Optional but recommended items glasses and gloves.

Preparation

For a quick and simple battery recharge, there are a few steps you can take to get everything prepared.

  • Determine what kind of battery your vehicle actually has to make sure you have a compatible charger. You can look on the battery itself or online for details. This information should tell you the voltage and type. 
  • Park the car in a safe location. Garages are ideal when charging the battery. Make sure the car is secure with the emergency brake. 
  • Confirm the battery needs to be recharged. Some starting issues may not be due to a dead battery, so double check the connections between the battery and the vehicle.

How to Recharge a Car Battery

Charging with a Battery Charger

The main way to recharge a car battery uses a specialized charger that can monitor the battery’s energy level as it charges. This way, there isn’t much of a risk of overcharging or damaging the battery. 

Disconnect the Cables

To get access to the battery’s terminals, you’ll have to remove the existing cables that connect the battery to the car.

  • Detach the negative cable from the negative post. The post will have a minus or NEG sign on it. 

Some batteries require a wrench to loosen the cables.
Make sure you don’t remove the positive terminal first. This can cause a short circuit.

  • Detach the positive cable from the positive post. The post will have a plus or POS sign on it.
  • (Optional) Clean the connections if necessary. You may need to remove corrosion or dirt. Water, baking soda, and a wire brush usually do the trick.

Avoid touching the terminals with your bare skin.

  • (Optional) Remove the battery completely. This is rarely needed, but you may find that taking the battery out will make it easier to position the charger next to it if the cables are short.

Charge the Battery

Once the battery is disconnected, you can hook up the battery charger and start the charging process. 

  • Place the charger next to the battery. It’s best to find a stable surface so the charger doesn’t fall off.

Don’t place the charger directly on the battery. We recommend using the full length of the cable to space the two if possible.

  • Connect the positive cable to the positive terminal. The post will have a plus or POS sign on it.

Make sure the cable is secured to the terminal.

  • Connect the negative cable to the negative terminal. The post will have a minus or NEG sign on it.

Make sure the cable is secured to the terminal.

  • Calibrate the charger. This step will depend on your particular charger, but you’ll need to indicate the appropriate voltage and charging mode or speed. Some chargers can determine these settings automatically from reading the battery.
  • Allow the battery to charge. This can take several hours.
  • Check the battery’s charge. Many battery chargers have a readout with the battery’s existing level. It should read “100%.”

If your charger doesn’t have a readout, use a voltmeter instead. You’ll need to connect the appropriate ends to the terminal to get a read. Consult the battery’s online information to find a voltage charge.

  • Detach the negative charger cable from the negative post
  • Detach the positive charger cable from the positive post.
  • Connect the positive car cable to the positive terminal.
  • Connect the negative car cable to the negative terminal.

Charging Through a Jump-Start

Jump-starting a car does more than getting it running again. If you leave the cars connected for a while, the good car can actually charge the dead battery a bit. This isn’t the best way to charge a car battery, especially if you want a full charge, but it can get you out of a pinch.

Connect the Cables

The first step is to get the jumper cables connected to the right posts on each battery. This involves some color matching. To connect the cables to the batteries:

  • Lift and secure the hood on each car.
  • Connect the red clamp on each end of the cable onto the positive terminal of each battery. The post will also be red and may have a “+” sign somewhere.
  • Connect the black clamp on the good car’s side onto the negative terminal of its battery. This post will be black and may have a “-” sign somewhere.
  • Connect the black clamp on the dead car’s side onto an unpainted, grounded metal part or surface. Somewhere on the vehicle’s frame is usually good enough. 
    • Do not attach the black clamp to the negative post of the dead battery. Doing so can create sparks. 

Turn on the Good Car

Once everything is connected properly, you can have the driver of the good car turn on the engine and let it run for a few minutes. This will start to recharge the dead battery.

  • Start the engine of the good car.
  • Keep the engine running for several minutes. The longer the engine runs, the more your battery should charge. 
  • Turn the engine off
  • Remove the cables. Once you are ready to disconnect the cables, you should remove the clamps in reverse order: black clamp from the grounded surface, black clamp from the good battery’s negative post, red clamp from the dead battery, red clamp from the good battery. 

Tips

  • Use a trickle charger to maintain the health of your battery. Fast charging isn’t required, and a slow charge can actually improve the battery’s ability to hold a charge.
  • While you can recharge a battery that doesn’t have any water, you’ll need to maintain the battery so it can keep a charge. 

FAQ

Q: Can I charge a completely dead battery?

A: Most batteries aren’t designed to be charged from a completely dead state. Some battery chargers, however, do have the capability to restore a dead battery to a full charge. 

Q: How long does it take to charge a car battery?

A: This depends on the charge level and its condition, but most chargers can take up to 24 hours to hit the full mark.

Q: Does my car recharge the battery?

A: There is an alternator in the car’s engine that charges the battery.