Ask any acknowledged lead-acid battery expert this question - Assuming a lead-acid battery is correctly maintained, correctly used, why does it wear out?
Answer: The lead-acid system is subject to slow, progressive corrosion of the positive grids when correctly used. It is subject to sulfation when it is persistently undercharged, (incorrectly used).
A lead-acid battery can give between 4 and 25 years service when it regularly receives a small, controlled overcharge. It can fail within 2 years if persistently used below full state of charge.
A large percentage of leisure marine, light aircraft, truck and automobile batteries are operated almost permanently below optimum state of charge, hence become sulfated.
This does not mean lead-acid batteries will naturally become sulfated, as implied by desulfation merchants. They have products to sell, therefore they will say whatever it takes to sell their products
The dividing line between corrosion and sulfation is a knife edge. There is no safe area of operation. The only way to make batteries last is to subject them to regular, mild overcharging.
The corrosion process begins when a lead-acid battery is formed. The lead at the surface of the positive grids is converted into lead dioxide. Lead dioxide passivates the metal surface. After that it takes many years in service for the layer of passivation to very slowly work its way right into the grids and cause them to fail.
Corrosion is necessary. The process of charging “corrodes” lead sulfate of the discharged positive active material into lead dioxide. The lead-acid system cannot work without corrosion. Undercharging causes lead that is exposed to sulfuric acid to be converted into lead sulfate. If there is no “beneficial” corrosion, there will always be “harmful” sulfation..
