How to Charge a Car Battery

Need to know how to charge a car battery? Charging a car battery isn't tricky if you've got a good battery charger and a safe place to perform the task. You'll want to make safety a priority as you tackle this job for the first time.

Follow these simple steps to safely charge your car battery:

  • Read Manufacturer's Instructions: Take the time to read the directions, even if you think you know what you are doing. There may be precautions specific to this particular battery or battery charger.
  • Fill a Bucket: Make sure you have a bucket of clean, soapy water nearby in case of an accident. If battery acid leaks onto your skin at any point, you need to wash with soapy water immediately. If you get battery acid in your eye, you will need to flush it with fresh, clear water for at least 15 minutes and call 911 for medical assistance.
  • Remove Jewelry: Remove all metal jewelry before attempting this task. Electricity can arc from the battery across your jewelry, causing burns and potentially causing the battery to explode.
  • Wear Proper Eyewear: Put on your safety goggles, eyewear that protects your eyes from every angle. Regular glasses are not protective enough.
  • Open up the Garage Door: Make sure you charge in a ventilated area. Never charge your battery in a closed area. Move the car outside or have the garage door open.
  • Remove Flammable Substances: Make sure there are no flammable substances anywhere near the battery or charger. This includes flammable cleaners, solvents and cans of gasoline. Sparks can fly while you're charging the battery, igniting vapors. Be careful not to cause sparks by allowing tools to touch either the battery post or the metal parts of the car.
  • Add Water: Add water to the battery cells until battery acid is covering the plates in each cell. Be careful not to overfill; always pay attention to level markers.
  • Place the Charger at a Proper Distance: Place the charger as far away from the battery as possible, without stretching the cables too much. Make sure the charger is switched off. Do not plug it in until it's connected.
  • Make Note of Voltage and Charge Rate of Battery: Most batteries are either 6 volt or 12 volt. Most charge rates are 2, 6, 12 or 30 amps. Set your charger appropriately. Too much current could cause the battery to explode.
  • Secure Charger Clips: Connect the positive charger clip to the positive post of the battery. Connect the negative charger clip to the engine block or the car frame, well away from the battery. If there's any charge in the system, you may get a small spark when you connect the second cable. The positive clip should be red; the negative clip should be black. Make sure each charger clip has solid contact by twisting them a bit.
  • Plug the Charger Into an Electrical Outlet: Don't do this until both clips are securely attached. Always make sure the battery charger is properly grounded; it should have an electrical cord that is equipped with a grounding conductor and a grounding plug. Never alter the cord. If you feel even the slightest shock when you plug in the charger, turn off the electricity and call an electrician to see if the problem is the charger, the grounding mechanism or the outlet.
  • Let the Battery Charge: The owner's manual for your charger should tell you how long it will take to charge the battery. Don't let the charger run too long, as this can overload the battery. Stopping the charger too quickly will leave you with an inadequate battery charge. If your battery isn't working properly after the recommended charging time, there's likely something wrong with the battery itself. 
  • Unplug the Charger. Unplug the charger from the outlet, then turn off the power. Disconnect the charger clips from the battery, beginning with the black clip attached to the engine block. The clip attached to the battery is removed last.

Safety Precautions

  • Never charge a frozen battery. Heat from charging may crack the battery's casing, spurting battery acid everywhere. 
  • Check the battery for cracks and corrosion before charging. If you see cracks or excessive corrosion on the terminals, the battery is leaking and needs to be replaced.
  • Never overcharge a battery. Batteries can explode or cause fires if they're overcharged.
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