¿Porque se sulfatan los bornes de la batería?

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Why are the battery terminals sulphated?

Sometimes, the terminals, terminals or poles of the lead-acid batteries corrode and a kind of white crystals appear around them, which gradually deteriorates the electrical connection until it finally restricts the ignition of the starter motor. Then the popular sound of trac, trac, trac appears, when we pass the suiche to the START position. This sound tells us that there is not enough current from the battery to run our starter motor, and you will see a decrease in the brightness of the indicator lights on the board.


Not necessarily the corrosion indicates that the battery is damaged, this is very important to have it clear and I already explain why this phenomenon appears and how to avoid it.

battery terminals sulphated chica mecanica

Causes and formation of compounds:

A battery is composed of lead and sulfuric acid diluted in water, this union of components is called electrolyte. The chemical reaction releases electrical energy and can also store it. Corrosion only occurs when sulfuric acid leaks from the battery's internal electrolyte to the terminals and this can occur for some of these reasons:

Flooded battery: The battery was filled beyond the recommended level. The excess escapes through the ventilation grilles.

Battery reheated: The temperature increases the volume of the electrolyte and raise the levels until it escapes through the grilles or ventilation holes. This is why it is advisable to protect the battery from direct heat from the motor with some shielding if possible.

Over charge of the battery. Voltages above 14.5V increase the electrolyte temperature and volume. This is because already the electrolyte saturated with electrons, can not receive more charge and to compensate, there are internal losses (internal battery resistance) that consume the energy of overload and dissipate in the form of heat and the battery will bubble. It is a very dangerous condition, since hydrogen gas is produced, highly explosive.

Top of dirty battery with a lot of dust: It is normal, the evaporation of water, which carries some sulfuric acid in droplets that escapes through the ventilation of free maintenance batteries, for example. These micro drops are condensed in the dust and dirt on top of the battery and the problem starts when it accumulates.

Cracks or cracks in the electrolyte container or terminal base: It is possible that if there is any crack or defect in the sealing of the battery acid leakage occurs. For this reason it is not advisable to hit the terminals or apply pressure to them so as not to damage the base seal that causes electrolyte leaks.


In the following image you can see some examples of sulfation:

A - Leakage either by evaporated gases or bubbling through the electrolyte container lid, condenses in support.

B - Splash of non-neutralized acid in battery terminal. This could have happened when the battery was filled with fluid, or some overheating or bubbling of the ventilation splashed the terminal.

C - Dirt and leakage on top of the battery. The hydrated copper sulfate is seen in blue, near the battery terminal.

Now, we have already seen how the acid can escape and be deposited in the terminals or terminals of our battery. So now I will explain a little what happens.

Lead itself is a stable metal, its reaction with sulfuric acid is very slow. If contact occurs at the battery terminals, the compound that forms as a result of the reaction is lead sulfate (PbSO4). The chemical reaction between lead and sulfuric acid is, therefore:

Pb (s) + H2SO4 (aq) → PbSO4 (aq) + H2 (g)

The white substance that is seen around the terminals of the battery is lead sulfate made from the reaction explained above.

Also, copper terminals may be used for the connection of the battery terminals. Copper itself is not reactive, even if diluted sulfuric acid is poured on it. But when the electricity passes, it reacts with the sulfuric acid producing copper sulfate (CuSO4) together with water and sulfur dioxide. The equation of this chemical reaction is the following:

Cu (s) + 2 H2SO4 (ℓ) → CuSO4 (aq) + 2 H2O (ℓ) + SO2 (g)

The bluish substance that is seen around corroded copper terminals is hydrated copper sulfate. Copper sulfate is poisonous, you have to be careful with it.

Cleaning corroded battery terminals


Cleaning is a fairly simple procedure.

1.- Disconnect the battery from its terminals.

2.- Wash affected terminals with abundant water. Protect your hands, since chemicals affect the skin.

3.- If the leakage of acid affects the terminals a lot, you have to neutralize it by spraying some liquid that is a base, as it is a solution of baking soda, milk of magnesia, carbonated soda or some cleaning product that is for sale. If it does not neutralize it, the sulphate will appear again in the terminal.

4.- After cleaning with the base solution to neutralize the sulfuric acid, re-wash the terminals with clean water to remove the remains of the base.

Important: DO NOT VIEW NONE OF THESE BASE SOLUTIONS ON THE BATTERY. The liquid can enter the interior of the battery through the vents, joints or leaks. If it is entered, it can seriously affect the performance of the battery. Instead, use a cloth moistened with a base solution to clean the top of the battery or use a brush to rub the sulfate. Take extra precautions when cleaning hydrated copper sulfate that is bluish in color because it is poisonous.

Prevention of corrosion:

1- Corrosion can occur in a dry environment, but is stimulated by moisture and salts present in the water. Therefore, keep the batteries clean, away from moisture and damp places.


2- Always keep the top of the battery dry and free of dust and other contaminants. After pouring water into a flooded lead acid battery, never forget to dry and clean the surface of the battery. Close the caps of the individual cells tightly to avoid accidental leaks.

3.- Do not fill the battery beyond the recommended level.
fill the battery beyond the recommended level
4- Apply Vaseline or grease to the terminals of the battery to protect them from corrosion. If there is no oxygen from the air, there is no chemical reaction.

5- Use battery terminals made of good quality copper that are also coated with alloy. The alloy layer prevents the terminals from corroding easily by the circulation of electrical energy.

Well, that's all. Soon I will make another article about the internal sulphation of the battery.

Written by
Dennis García
Chica Mecanica.

Muy completo.

Lo dice todo Dennis, excelente articulo.

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    ¿Porque se sulfatan los bornes de la batería?

    ¿Porque se sulfatan los bornes de la batería?

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    4 Question(s) answered

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    • Asked by Juan zambrano
      on 01/16/2019
      Buenas, saludos para todos, me gusto el articulo expuesto aquí, gracias de verdad muy bueno, una pregunta si cada vez que apago mi vehículo le desconecto el borne positivo y lo dejo asi hasta el otro día ¿ es perjudicial para la batería o para el vehículo ? Les agradezco algún comentario al respecto, gracias de antemano. Answer:
      Que tal Juan, muchas gracias por tu comentario. : ) . No hay ningun problema, por lo general siempre aunque el suiche este apagado, siempre, sobre todo en los carros nuevos (del 95 para aca) consumen algo de energía. Pero una batería en buen estado puede suplir este consumo por varios dias sin descargarse demasiado. Lo único desfavorable de tu operación es que los accesorios del carro pierden la configuración, como el reproductor de sonido, la hora del reloj, etc.
    • Asked by Pedro Marzano
      on 02/22/2019
      Hola chica! me gustan tus videos. Una pregunta, yo limpio la bateria y me sigue saliendo sulfactación en los cables donde estan los bornes. ¿Como hago para que se elimine? ¿O es que esta dañado algo? Answer:
      Bueno Pedro, en esos casos donde la sulfatación llega a los cables tienes que picar el trozo afectado si puedes, es decir si tienes cable suficiente. Sino, debes retirar el aislante y dejar el cobre libre hasta donde este afectado y lavarlo con agua con bicarbonato muy bien para neutralizar el ácido. Luego vuelves a cubir la parte donde retiraste el aislante con termoencogible o cinta aislante. Y listo.
    • Asked by Luis
      on 02/26/2019
      Cómo rotar las baterías cuando son dos ?? Answer:
      Que tal Luis, ¿Rotar dos baterías?
    • Asked by Jean Bolivar
      on 08/25/2019
      ¿Como me pongo en contacto con chica mecánica para que me revise mi auto chery orinoco? Tiene falla que no me deja acelerar más 40Km/h y me enciende la luz del ESP (triangulo con circulo amarillo) Adicionalmente, al frenar el pedal de freno se sienten algunos golpecitos levesAyuda chica mecánica!!!! Answer:
      Puede ser por instagram o email a intarce@gmail.com. ¿El carro es automático?

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