When car batteries aren't used for a long period of time, they lose their ability to hold a charge. Over time, the lead from the batteries' internal plates combine with electrolytes to create lead sulfate. When this happens, you must completely desulfate the battery so that it again holds a charge. Desulfation is also known as battery "reconditioning." Because batteries contain toxic chemicals, such as lead acid, you must take safety precautions. Always wear goggles and gloves when performing this procedure.
Remove the Battery
Put on the gloves and safety goggles.2
Ensure that your vehicle is in "park." Open the hood by pulling the latch that's located under the steering wheel; the latch is usually on the left side of the area under the steering wheel. Make sure that the hood stays up by connecting the hood's adjustable rod to the rod port, if necessary.3
Read your vehicle's owner manual to see whether the car battery has a "negative ground," as most batteries do. Negative ground is signified by a "-" or "NEG" on the battery terminal. Positive ground is signified by a "+" or "POS". If the battery has a "positive ground," disconnect this cable first. Loosen the nut and bolt on the clamp that holds that battery cable on the positive terminal. Remove the cable.Then disconnect and remove the cable to the negative terminal.4
Remove the device that holds the battery in place using an appropriate screwdriver. For example, the device may hold the battery in place using a number of Phillips-head screws. Loosen the screws using a screwdriver. Finish unscrewing the screws by hand so that you don't lose them. Remove the battery.
Complete the Desulfation Process
Measure 7 to 8 oz. of Epsom salts. Heat 1/2 quart of distilled water to 150 degrees Fahrenheit. Test the boiling temperature using your thermometer. Pour the Epsom salt into the hot water and let it dissolve.6
Put on your gloves and goggles again if you removed them. Remove the caps on the battery cells. If the battery is sealed such that you can't see the battery cells, locate the "shadow plugs" that cover the battery cells. The shadow plugs are drawn onto the battery compartment itself. Slowly drill through the outline for each shadow plug until you can see the cells.7
Drain any remaining battery fluid into the bucket. Neutralize the fluid by pouring baking soda into the fluid. Dispose of the neutralized acid by pouring it down a drain. Turn on the water and slowly pour the neutralized acid down an inside or outside drain. This procedure is safe, as you've neutralized the fluid with the baking soda.8
Use plastic funnels to pour Epsom salt into each battery cell until the cells are filled with salt. Replace the battery caps on the battery. If you drilled holes into a sealed battery, you must plug plastic plugs into those holes. Gently shake the battery to ensure that the Epsom salt is well distributed.9
Read the instructions for your individual battery charger. Each charger works differently. Charge the battery by connecting the positive --- "+" or "POS" --- cable to the positive terminal; then attach the negative cable to the negative terminal. Charge the battery according to your battery charger user instructions. Select the correct "VOLT/AMP" setting on your charger. The battery is desulfated after the charge is complete.