How To Recondition A Car Battery

(Last Updated On: March 15, 2024)

Car batteries can depreciate over time, get adversely affected by constant deep discharges, high temperatures, and other environmental threats. Being able to rejuvenate a car battery could prolong its lifespan and regain its maximum capacity.

When a battery stops holding a charge or loses capacity, the reason is often sulfation. This happens when lead sulfate crystals accumulate on the plates inside the battery. Most of these particles are re-converted into usable lead when the battery is recharged, but some are left behind. 

How to recondition a car battery
Battery reconditioning can prove to be quite a challenge

Over time, the accumulation of these particles lowers the battery’s ability to hold a charge. Desulfation is the process of removing these particles, turning back the clock on your battery’s aging process. You’ll also hear this process called battery restoration and battery reconditioning. 

Many auto shops will restore your battery for you, for a small fee. You can also recondition a battery at home, however, and you don’t need to be an auto expert to do it. 

Why do you need to know how to recondition a car battery?

Reconditioning your car battery at home can be a huge money saver, especially if you own multiple vehicles. Battery reconditioning gives you a more usable life. This means you won’t have to replace your battery as frequently—and will likely get better performance from it, too.

It’s also important to know how to recondition a battery correctly. If you don’t follow the right steps, you could do more harm than good. Then you’ll be stuck buying a new battery, anyway—along with wasting a couple of hours of your time. 

Can all batteries be reconditioned?

Most lead-acid batteries can. This includes AGM, gel, and any battery based on the lead-acid concept. If you have another style of battery, like lithium-ion, you can’t recondition it using the steps outlined here. 

Traditional car batteries contain a series of plates contained in a liquid or gel electrolyte solution. The charge is generated by the reaction of the solution to the plates. Some corrosion of the battery plates caused by sulfation is irreversible. This is why most batteries can only be restored three to five times before dying completely. 

The easiest way to find out if your battery will respond to reconditioning is to test it with a digital voltmeter. A functioning car battery should read 12 volts. If the battery reads between 10 and 12 volts, it will likely come back to life with reconditioning. A reading lower than 10 volts usually means the battery is beyond redemption. 

How to recondition a car battery at home

Before you get started, make sure you have all the supplies you need, including:

  • ½ quart distilled water
  • 8 ounces magnesium sulfate (Epsom salts)
  • Plastic funnel
  • Trickle charger
  • Rubber gloves
  • Safety goggles

If your battery is sealed, you will also need a hand-held drill to access the interior, and plastic plugs to put into the holes after you’re finished. Once all of your supplies are assembled, the steps are easy:

  1. Remove the caps of the battery cells. If the battery is sealed, find the shadow plugs, or the covers of the battery cell openings. This is where you’ll need to drill to access the battery interior. 
  2. Heat the distilled water until it reaches 150°F. Stir the Epsom salts in until they dissolve.
  3. Drain any fluid remaining in the battery. Keep in mind that the liquid inside a battery can be harmful, so you shouldn’t pour it directly on the ground. Use an oil draining pan, and dispose of any waste liquid properly. 
  4. Use the funnel to pour the Epsom salt mixture into the battery, filling each cell.
  5. Replace the battery caps (or insert the plastic plugs, in a sealed battery). Make sure they’re firmly inserted, then gently shake the battery to distribute the Epsom salt across all the surfaces. 
  6. Attach your battery to a trickle charger for at least 24 hours to restore it enough to start your car. At this point, you can reinstall it in your vehicle. 

How to recondition a car battery that won’t hold a charge

If a battery won’t hold a charge, there could be more wrong than just a sulfation problem. There are a few extra steps you should take to recondition a car battery that won’t hold a charge. 

  1. Test the battery with a voltmeter after taking it off the charger to see if it is charging. The reconditioning may have restored the charge. If it didn’t, continue with the steps below. 
  2. Test the battery cells with a hydrometer. Squeeze the bulb, the insert the tube into one of the battery’s cells. Check the color of the solution you draw out. If it’s dark, the cell itself is bad and you should replace the battery. 
  3. Pull the fluid into the scale of the hydrometer and check the color. If it’s green or white, the battery is salvageable. A red reading indicates the cell needs to be charged.

If the battery was dead or wouldn’t hold a charge, it may need more time on the charger before you reinstall it. Leave it on the charger for 3-4 nights. This should restore it to full capacity. 

Tips for safely reconditioning a car battery

  • Don’t use tap water or mineral water when reconditioning a battery. Tap water often contains trace minerals and chemicals that can react with the electrolyte mix, or otherwise impair your battery’s function. Use only pure distilled or filtered water in your battery.
  • Always wear safety goggles and rubber gloves when working with your battery. The sulfuric acid contained in car batteries is highly corrosive. If you do get any on your skin, wash it immediately with cold water.
  • Never work with your car battery around open flame or in high heat. Heat increases the reaction inside a battery and can make it unsafe to work with.

The bottom line

Knowing how to recondition a car battery can save you a lot of money and hassle in the long term. It’s also a relatively easy DIY project, as long as you follow the right steps and safety precautions. While not every battery can be reconditioned, for most it will restore power and longevity.

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