Reconditioning a lead-acid automotive battery prolongs its life, unless it has deteriorated irreversibly. Most battery failures occur when crystalline lead sulfate builds up on the lead plates inside the unit, preventing it from storing electrochemical energy during charging. Removing sulfation, as this buildup is called, restores the internal chemical balance and allows the battery to hold a normal charge.

 

1. Examine the exterior of the battery closely for any physical damage. If the battery casing is split or cracked, or if the terminal posts are loose, it is unlikely that you will be able to recondition it economically.

 

2. Clean the terminal posts with a battery post cleaner. If the battery has side terminals, use a wire brush. Connect the positive lead of a voltmeter to the positive battery terminal and the negative lead to the negative terminal. Note the battery voltage, which should be between 11.5 volts and 12.6 volts for a 12-volt battery, and between 5.8 volts and 6.3 volts for a 6-volt battery. If the voltage is below 10.5 volts or 5.25 volts, respectively, the battery is probably not suitable for reconditioning.

 

3. Remove the caps from the battery cells. If you have a sealed battery, examine the top of the case and identify the area immediately above the plates in each cell. Put on suitable protective clothing, including safety goggles, and drill a small pilot hole through the top of the case into each cell. Use successively larger drills until you have a 1/2-inch-diameter hole. Do not drill into the plates or you will damage the battery, making it useless.

 

4. Put on heavy-duty rubber gloves and a plastic or rubberized protective apron. Place the battery into a large plastic bin. Taking great care, tip the contents of the battery into the bin. In addition to the electrolyte, tip out any sludge that has accumulated in the cells.

 

5. Place the battery on a level surface. Using a plastic funnel, fill each of the cells with distilled water to a level just above the plates. Replace the caps on the cells. If you drilled holes in the top of the case, fit a rubber bung securely in each hole. Shake the battery gently to agitate any remaining sludge, holding it above the plastic bin while you do so. Remove the cell caps or bungs and empty the battery carefully into the bin. Repeat this step if necessary to remove as much sludge as possible.

 

6. Pour two liters of distilled water into a pan. Add 500 grams of sodium sulfate, or Glauber’s salt and heat the water gently, stirring until the sodium sulfate is dissolved. It is not necessary to boil the water. Remove the pan from the heat and allow the solution to cool to room temperature.

 

7. Fill each of the battery cells with sodium sulfate solution to a level just above the plates. Ensure the battery is level during filling. Place the battery in a well-ventilated area ready for charging and leave it to settle for at least 30 minutes. If the battery has side terminals, fit charging posts to the terminals.

 

8. Connect the positive lead of a battery charger to the positive battery terminal and the negative lead to the negative terminal. If you have a dual-mode charger, set it to "Constant-Current" mode. Turn on the charger and monitor the current. If the current output is adjustable, set it to no more than 20 percent of the rated capacity of the battery in ampere hours. For example, if you have a 40-ampere-hour battery, the current should not exceed 8 amperes.

 

9. Charge the battery for up to 12 hours. Measure the charging voltage at 2-hour intervals and stop charging if it reaches 14.5 volts. Check the battery temperature at the same intervals and stop charging temporarily if the case feels hot when you touch it. Resume charging once the battery has cooled.

 

10. Turn off the charger and disconnect the charging leads from the battery. Remove the terminal posts if fitted. Check the level of electrolyte in each cell and top up with distilled water if the plates are not covered. Replace the cell caps or bungs.

 

11. Check the battery voltage, which should be about 12.6 volts for a 12-volt battery, and 6.3 volts for a 6-volt battery. Test the battery with a load tester in accordance with the manufacturer’s instructions. If the battery voltage is correct and the battery passes a load test, the reconditioning has succeeded.

 

12. Spray the battery case with battery cleaner and wipe clean. Apply a thin film of light grease to each terminal post before putting it into service. Arrange safe disposal of the fluids that you drained from the battery.