If your car’s battery isn’t holding a charge or otherwise is not up to par, you may be able to fix it. The most common cause of degraded battery performance in lead-acid batteries is sulfation, which occurs when sulfur collects on the lead plates in the battery, blocking the electric current. It’s not difficult to recondition a car battery at home. However, sulfation causes irreversible corrosion of the lead plates, so this process will work only three to five times. Test the battery to see if it is likely to respond to reconditioning; it needs to register 12 volts on a voltmeter. If it’s between 10 and 12 volts, you may be able to restore the battery to full function, but if it tests at less than 10 volts, you’re probably wasting your time.
Heat a half quart of distilled water to 150 degrees F, and dissolve 7 or 8 oz. of Epsom salts in the water. Remove the battery cell caps. If you have a sealed battery, find the “shadow plugs” that cover openings to the battery cells--you’ll need to drill through these. Drain any fluid out of the battery and use a plastic funnel to pour enough of the Epsom salt solution in to fill each cell of the battery properly.
Insert plastic plugs in the drill holes or replace the battery caps and shake the battery to make sure the Epsom salts solution is well distributed. Recharge the battery on a slow charge for 24 hours and then re-install it in your car.