If you have an automotive or other lead-acid battery that isn’t working properly, you may be able to recondition it. Lead-acid batteries decline in performance most often because sulphur accumulates on the lead plates of the battery, corroding them and blocking electric current flow. You can use a common household chemical, magnesium sulphate (Epsom salts), to recondition a lead-acid battery. If you follow the proper procedure, the magnesium sulphate will remove the sulphur and restore the battery to normal operating condition.
Heat a half quart of distilled water to about 65.6 degrees C and add 198 or 227g of Epsom salts. Stir until the Epsom salts are completely dissolved. Do not use tap water because it contains chemicals that will contaminate the battery.
Remove the battery caps and carefully drain the water from the battery. If you have a sealed (low-maintenance) battery, find the access points (also called shadow plugs) and use a drill to open them. Insert a funnel and pour enough of the Epsom salts solution in to refill the cell. Repeat until you fill each cell.
Replace the battery caps. Use plastic plugs to close up the drill holes in a sealed battery.
Shake the battery vigorously for a minute to make sure the solution works its way through each cell.
Place the battery on a charger and allow it to charge slowly for 24 hours. To completely recondition a lead acid battery, you may need to charge it to capacity several times over the next few days.
You can recondition a lead-acid battery only three to five times because each time the lead plates become coated, some irreversible corrosion takes place. If you are going to store the battery for several weeks or more, place it on a solar or other trickle charger.
Follow safety precautions. A lead-acid battery contains sulphuric acid. Wear safety goggles and rubber gloves, and work only in a well-ventilated place. If you get any liquid from the battery on you, immediately wash the area with water and apply baking soda to prevent chemical burns. Test the battery to see if it’s worth reconditioning with a voltmeter with a wire probe. You may be able to revive a 12-volt battery if it’s showing over 10 volts, though your chances are best if it’s registering 12 volts.