How to Recondition a Car Battery

Beverly Braga | Oct 29, 2020

All cars need a battery, whether they have internal combustion engines, are hybrids, or are electrics. But the battery is also one of the many things in our vehicle that we take for granted until the car doesn't start. Turn the key all you want or repeatedly push the ignition button, but a dead battery is a dead battery.

How to recondition a car battery

Vehicles with an internal combustion engine (ICE) rely on standard flooded lead-acid batteries — those familiar 12-volt black boxes. Hybrids add a larger nickel-metal hydride (NiMH) or a lithium-ion (Li-ion) battery to power a small electric motor that helps an ICE improve fuel economy. Then we have our plug-in hybrid and electric vehicles, which are typically equipped with sizable Li-ion battery packs to offer pure electric driving range.

Back to the dead battery dilemma. For this article, we're talking about the 12-volt lead-acid batteries, and when one goes dead a jumpstart or battery recharge is the obvious solution. With traditional batteries, it's also just easy (but perhaps costly) to visit a local automotive parts store or big-box retailer to purchase a replacement. But what if instead of replacing the battery every time it died, you could simply recharge it to full strength — and do so several times?

What is Battery Reconditioning?

In supplying energy to a vehicle or device, a battery discharge process known as sulfation occurs. This chemical reaction leads to a build-up of sulfate crystals on the battery plates. More crystals mean longer charging times, less efficiency, and lower charge capacity. Reconditioning, or refurbishing, a battery cleans off these sulfates, replenishes the electrolyte solution within, and allows the battery to recharge and function like new.

How to Recondition a Car Battery at Home

The following will be specific to lead-acid batteries. Although you don't need to wait until a battery is depleted to recondition it, put safety first. A quick visual inspection will determine whether the battery is viable for reconditioning. Check for cracks, bulges, or broken pieces of any kind. If the battery is not in good physical shape, it is best to purchase a new one.

The process of battery reconditioning does not require an engineering degree, although it does take patience. Most of the items you'll need you're likely to have at home. Below is the essential list of supplies:


  • Protective wear (e.g., safety goggles, chemical-resistant gloves, apron)
  • Toothbrush
  • Steel wool or battery terminal cleaner
  • Flathead screwdriver
  • Funnel
  • Two large buckets


  • 1 gallon of distilled water (no tap water due to chemicals added)
  • 1 pound of baking soda
  • 1 pound of Epsom salt

Specialty items:

  • Battery charger
  • Voltmeter

Step-by-Step Guide to Reconditioning a Battery

Suit up and space out –This might not be rocket science, but it's still science. Things could get messy. Make sure you're working in a well-ventilated area, too.

Create a cleaning solution – Use a 2-to-1 ratio of baking soda to water to create a runny paste. This mixture will serve as a battery cleaner as well as an acid spill cover-up.

Clean the battery – If the battery terminals are corroded, apply the cleaning paste (or a dedicated battery cleaning product) to the posts and scrub the build-up off with a toothbrush. A foaming reaction means the solution is working. Use steel wool for heavily-corroded batteries. Clean, wipe, and dry off the terminals completely.

Verify the voltage – Connect the voltmeter. Like jumpstarting a car, the red cable connects to the positive terminal and the black cable to the negative terminal. A standard car battery contains six cells, each producing about 2.1 volts. Therefore, a healthy battery will read 12.6V. Between 10V and 12.6V will mean you can recondition the battery. At less than 10V, replace the battery instead.

Empty the battery cells – Until now, you did not need to remove the vehicle's battery. At this point, however, you should. Have a bucket and a half-pound of baking soda nearby. Take the battery cover off and use the flathead screwdriver to remove the cell caps underneath. One by one, slowly empty the cell contents into a bucket. You can add baking soda as you go or after all the cells are empty. Either way, it will neutralize the battery acid for safe disposal at any facility, like a recycling center, that accepts hazardous waste.

Clean the battery cells – Using the funnel, pour the cleaning solution into each cell. Securely replace the cell caps and battery cover. Now shake the battery for at least a minute. Unseal and dispose of the mixture into the existing old-acid waste bucket.

Replace battery cell solution – Mix 4 cups of water with 4 ounces of Epsom salt. Stir until the water is clear. Boiled water speeds up the process but isn't necessary. With the funnel, refill the cells with the new electrolyte solution. Cover and re-shake to evenly distribute the salt.

Recharge the battery – Like a good brisket, perform this step low and slow. Set up in a safe and secure area. As an extra precaution, remove the battery caps again as the electrolyte solution will heat up and may overflow during charging. Place the charger as far away from the battery as possible and connect it at a speed of 12V / 2 amps. Let the battery recharge for 36 hours.

Test the battery – Disconnect the charger and use the voltmeter to check the battery's status. Normal readings are about 12.42V. If yours is lower, charge it again for another 12 hours. When you're good to go, perform a load test by reinstalling the battery and turning your vehicle to the "On" position and with the high beams on. After a few minutes, test the battery again while it is under load. If the voltmeter readout lists 9.6V, congratulations! You've successfully reconditioned your car battery.

How long a reconditioned battery will last is relative to its age and existing capacity. In theory, you should be able to repeat this process a few more times, which means extending the battery's lifespan beyond the typical three to five years.

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