How to Restore a Car Battery

If you have an old car battery that has a low voltage output, it might be time to consider a small restoration project. Reviving worn- out car batteries is an important money and time-saver – and one that could save you from hardships in the future. Below, we take a look at how to refurbish a car battery and why it is so important.

When Should I Restore My Battery?

Car batteries are types of lead-acid batteries. This means they have lead-acid cores that can suffer a condition called sulfation over time. Sulfation occurs when sulfur accrues on the lead plates that reside inside the battery casing. It can be caused by overcharging, storing a battery at temperatures above 75°F or storing a battery when it’s not fully charged. An excess of sulfur build-up on a lead acid battery plate will increase charge times and heat build-up while reducing run time between charges; eventually, it can cause the battery to fail altogether.

Luckily, if there isn’t an over-abundance of sulfur corrosion, a car battery can be restored. This is much preferred to replacing a costly battery. In order to determine whether or not you should restore your car battery, consider the following details:

  • If your battery can no longer start your car, it is time to restore it.
  • A battery shouldn’t be restored if it has any major physical defects like burnt connectors, melted plastic housings or warped battery sides. In this case, it is best to replace the whole battery.
  • Most car batteries today last an average of four years. If your battery is older than four years and/or has perpetual trouble starting your car, regardless of frequent charging, it should be restored.
  • If you check the battery’s voltage multiple times with a voltmeter and the charge is consistently below 12 volts, it has most likely suffered from sulfation and should be restored.

Note: the longer your battery has been in a low-charge state, the less likely you will be able to restore it. Being in this state for weeks or even months can lead to permanent sulfation in lead-acid batteries. You can still apply our “How to Restore a Car Battery” guide, but know that it is not always successful even if there is no other damage.

With these factors in mind, it is time to gather your materials and restore your car battery.

Restoring Your Battery

You will need the following items to perform your battery restoration project:

  • Baking soda
  • Distilled water
  • A power drill
  • Magnesium sulfate (commonly known as Epsom salt)
  • Non-metallic storage funnel
  • Non-metallic storage container
  • P lastic replacement plugs
  • Safety glasses
  • A three-phase battery charger for lead-acid batteries
  • Water
  • Work gloves
  • A wrench

The first thing to do is turn your car off and let your car battery cool for about an hour. Once the battery is cool, open the car hood and use your wrench to detach the negative battery cable first and then the positive cable. Be sure not to touch your wrench to any other metal part of the car to avoid experiencing a small jolt of electricity. Now, carefully remove the battery from the car.

Take off the plastic cell caps on the topside of the battery and find the location of the sealed cells inside the casing indicated by small marks. Put on your safety glasses and drill into the sealed cells using your power drill. Put your work gloves on and turn the battery upside down above a non-metallic storage container to drain the fluid inside. Add baking soda to the battery fluid in slowly paced increments of tablespoons to neutralize it. Once the fluid stops bubbling, close the container tightly and take it to a hazardous waste disposal site.

Now, take your Epsom salt and stir one part of it into three parts warm, distilled water until you have one full quart of magnesium sulfate solution. Insert your non-metallic funnel into one of the now-open battery cells and carefully pour some of your magnesium sulfate solution into the battery. Lightly shake the battery to evenly distribute the solution inside and let the solution sit. Repeat this step for the other cells as well.

Make sure your three-phase battery charger is off before you clip the positive lead onto the positive battery terminal and the negative lead onto the negative battery terminal. Set the charger’s dial to 12 volts and then turn on the charger. Leave the trickle charge going for at least 12 full hours before turning it off and unclipping the leads from the battery terminals. After this is done, return the caps onto their cells – or use your plastic plugs to cover up the drilled holes – and reinsert the battery into its place underneath the car hood. Once, you have reconnected the positive cable first and then the negative cable to their terminals, you have successfully restored the battery. It is best to repeat this entire process at least once a week for one whole month in order to ensure that any remaining deposited sulfur is dissolved. This way, your battery will be healthier and last much longer.

To learn more about car batteries and for various DIY car tutorials, be sure to visit Eastwood.com.

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6 thoughts on How to Restore a Car Battery

  • The lead is used in soldering the components in the circuit board.
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  • Louis Beaudreau, I have a question for you: You do not put acid and water back into the battery and you leave the magnesium sulfate solution in the battery?

  • This works…so far, it has been two weeks. Still holds charge. Done it just as it says. Just some baking soda, and epsom salt. Make sure you use distilled water.

  • I just did mine but put new battery acid instead of distilled water…have it hooked up to a 12 18watt solar panel for charhing..let’s see how it turns out.

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