How to Restore a Weak Car Battery

by Paul Dohrman
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You may find that for a car battery more than two years old or more, it may not hold its charge like it used to. Car batteries do have a finite lifespan. According to, only 30 percent of batteries sold today last a full four years because of the increased energy requirements of today’s cars. However there is maintenance you can perform to restore most of your car’s battery performance for a fraction of the cost of getting a brand new one.

Step 1

Turn off the ignition. Put on rubber gloves and safety glasses to protect against acid burn and a blinding explosion respectively. Remove the battery’s cables and put it someplace well ventilated for you to work on it.

Step 2

Remove the plastic cell caps on top if the battery is the serviceable type. If the cells are sealed, then drill a hole in the plastic, one hole for each cell. You’ll see where to drill because each of the six cells will have “shadow marks.” You’re going to plug these holes with “hole caps,” which most hardware stores will have.

Step 3

Microwave a quart of distilled water, to around 150 degrees. (If you overshot it and it’s boiling, let it cool a little first.) Don’t use tap water, since it may contain minerals that coat the battery plates and inhibit function.

Step 4

Dissolve 10 tablespoons of Epsom salts (magnesium sulfate) into the water.

Step 5

Pour the salt solution into the top of the battery through the six holes. Fill them up to the marked levels.

Step 6

Charge the battery overnight with a “smart charger.” You should especially use a three-step charger (see Resources) to make it fully charged. They are especially important since charging the battery with your car alternator alone can leave it only 90 percent charged. According to, the remaining 10 percent of the reactive electrolyte leads to sulfation (sulphur deposition on metal plating), the process that causes 80 percent of battery weakening in the first place. You can get such a three-step charger for around $40.

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