The working principle of a lead-acid battery involves positive and negative electrode reactions. The positive electrode reaction is: PbO2 + 4H+ + SO42- + 2e- = PbSO4 + 2H2O, and the negative electrode reaction is: Pb + SO42--2e- = PbSO4.

The overall battery discharge reaction is: PbO2 + 2H2SO4 + Pb = 2PbSO4 + 2H2O. Lead dioxide and lead react with dilute sulfuric acid to form lead sulfate and water, and the charging process is the reverse reaction.

The liquid added to the lead-acid battery is the legendary H2SO4, or dilute sulfuric acid. The battery is only filled with sulfuric acid when it is activated, and afterward, only pure water needs to be added. The main advantages of using a lead-acid battery with sulfuric acid solution are stable voltage and low cost; however, its disadvantages include low energy density, short service life, and frequent daily maintenance.

The lifespan of the old-fashioned ordinary battery is generally about 2 years, and it requires regular checks on the level of the electrolyte and the addition of distilled water. However, with technological advancements, the lifespan of lead-acid batteries has become longer, and their maintenance has become simpler.