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Is it possible to rejuvenate a car battery by adding more acid to it? I’ve heard that some dead batteries can be restored.
You might be thinking of older batteries, which need to be periodically checked and topped off with water. Most new batteries are maintenance-free, so you can’t mess with the components inside. Older battery designs lose water in the electrolytea mixture of about one part sulfuric acid and two parts waterfrom evaporation. If you have this kind, check it twice a year and add distilled water only as needed. Adding acid actually makes a battery deteriorate faster.
It comes down to how batteries work and eventually lose their ability to hold a charge. In a typical wet-cell design, a lead plate (negative) and a lead oxide plate (positive) are immersed in the electrolyte. A porous separator keeps the plates from touching and shorting out. Each pair of plates generates a certain amount of voltage, and multiple sets are combined for higher output. Drawing voltage from a battery causes the plates to react with the electrolyte, which forms lead sulfate; this chemical process creates water and releases electrons that generate current. Eventually the water dilutes the electrolyte, which can’t keep reacting, and that results in a discharged battery. Charging the battery reverses the chemical reaction and restores the plates’ chemistry.
The process deteriorates over time. The plates gradually build up oxidized debris that reduces their ability to react. This buildup is called sulfation. If you increase the acidity of the electrolyte, it accelerates sulfation.
Batteries generally have a life span of five years, and advanced designs can last seven to 10 years, so don’t feel too bad if your old battery makes its way to the recycler. You can extend the life of your battery by making sure it stays fully charged and avoiding rapid charging.