How to Charge a Car Battery at Home

Updated July 19, 2017

It happens to everyone sooner or later. For whatever reason, the car battery dies. Maybe something electrical was left on in the car and drained the battery. Maybe the battery is close to the end of its life. Or perhaps the alternator is dying and the electrical components of the vehicle are sucking the life out of the battery. Provided you have a battery charger and a length of proper AWG electrical extension cord (if needed), you can charge your own battery at home and save yourself incurred charges at local repair shops or auto parts stores.

Park the car in a well-ventilated place or even outside, weather permitting, if the battery you're charging is in the vehicle. Even if the battery is out of the vehicle, you should find a well-ventilated place to charge it.

Inspect the battery. Make sure there are no leaks coming from it. If it's in the car, make sure the terminal ends and battery posts are clean and not covered in corrosion. If they are, clean them thoroughly as corrosion could be the reason the battery is not getting charged by the alternator when running. If you notice the battery is leaking, do not attempt to charge it. It will need to be replaced and handled with great caution. If no leaks are present, plug the cord of the charger into the extension cord, but do not plug the cord into a nearby outlet yet. If you do not need an extension cord, do not plug the charger into the outlet.

Attach the black clamp of the battery charger to the negative post of the battery. Make sure you're attaching it to the negative post. Reversing polarity can damage the battery and even the car. Another option for the negative clamp for a battery that is in the car is a clamping it to a clean metal part of the frame or engine block away from any moving parts and away from the battery. Batteries have hydrogen gas that build up and a spark can create an unwanted ignition of that gas present resulting in an exploding battery, so wear safety goggles. As long as the battery charger is not plugged into the outlet, there should be no spark. Most sparks occur when applying and removing the live clamps of battery charges or jumper packs or cables. Placing the negative clamp away from the battery onto the frame or engine block is an attempt to move any possible spark away from the battery and not ignite the hydrogen gas. Apply the red clamp to the positive battery terminal or positive battery post.

Set the options on the battery charger. Determine the amount of volts you want to charge, the amount of amps you want to apply, and if equipped, the amount of time you want to charge the battery. The longer a battery can charge, the better. It depends on what you have time for. If you're limited, you may want to apply a higher amp and shorter time period. If you can charge the battery slowly (recommended) you can use a lower amp and a longer time period. Based on a battery that calls for 550 cold cranking amps, it would take approximately nine hours to charge a depleted battery at 6 amps on 12 volts. If the battery has some life left in it, it would take less. The more time you want the battery to charge, the less amps you need to apply. Most car batteries are 12-volt batteries and should be set as such on the battery charger.

Plug the extension cord or the power cord of charger into the outlet. If the charger has a timer switch, set it now and it will activate the charger. If it does not have a time option, take note of the time. Either option, try not to be facing the battery when you apply the electricity to the charger in case of ignition to the hydrogen gases. This is a rare occurrence, but it does happen.

Allow the proper time to pass and unplug the battery charger from the power outlet. Unclamp the red positive battery charger clamp. Unclamp the black negative battery charger clamp. If the battery was in the vehicle, test start the vehicle and allow to run. If it was not in the vehicle, install it and then test start. If the battery dies again, repeat the procedure or have a service station test the electrical system of your car. Chances are, something else could be wrong.

Things You'll Need

  • Medium to high quality battery charger
  • Long 18 AWG extension cord, if needed
  • Safety goggles (recommended)
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About the Author

Jody L. Campbell spent over 15 years as both a manager and an under-car specialist in the automotive repair industry. Prior to that, he managed two different restaurants for over 15 years. Campbell began his professional writing career in 2004 with the publication of his first book.