The electrochemical reaction of the lead-acid battery can be expressed in the following formula:

PbO₂+2H₂SO₄+Pb

PbSO₄+2H₂O+PbSO₄

(Lead dioxide) (sulfuric acid) (lead sea cotton) (lead sulfate) (water) (lead sulfate)

electrolyte

Positive active material, negative living material

Positive electrode discharge product, negative electrode discharge product

Ordinary lead-acid battery, in the later charging period, will occur water decomposition reaction, that is, from the positive electrode produced oxygen, the negative electrode produced hydrogen, and spread to the air, so it is need to often add water to compensate for the loss of electrolyte.Then in our VRLA battery, the oxygen generated by the positive electrode in the charge is compound at the negative electrode, the so-called "oxygen cycle" or "oxygen composite".

Positive electrode:

negative electrode:

H₂O

2H⁺+1/2O₂+2e-

Pb+1/2O₂+H₂SO₄

PbSO₄+H₂O

PbSO₄+2H⁺+2e-

Pb+ H ₂SO₄

In the above cycle, the net result is the decomposition of the positive electrode water, and the regeneration of water at the negative electrode. The specific expression is as follows: the electrolyte in the battery adopts the "greedy liquid" state, that is, about 5% of the microhole in the ultrafine glass fiber partition as a gas channel is not occupied by the electrolyte.When charging, the oxygen generated from the decomposition of the positive electrode water spreads along the airway to the negative electrode, reacts with the negative electrode sea cotton lead, and the resulting water returns to the electrolyte.The lead sulfate generated at the same time is then converted into lead during charging.Oxygen is combined at the negative electrode, and hydrogen is produced at the negative electrode, which is why VRLA batteries can be sealed and maintenance-free.