Working principle: When the sulphuric acid is dissolved, its molecules break up into hydrogen positive ions (2H⁺) and sulphate negative ions (SO₄^-) and move freely. Now if two lead electrodes are immured in this solution and connected to d.c. supply mains, the hydrogen ions being positively charged move towards the electrode connected to the negative terminal of the supply mains  (i.e. cathode) and SO₄^- -ion being negatively charged move towards the electrode connected to the positive terminal of the  supply main (i.e. anode). Each positive hydrogen ion (H⁺) reaching the cathode gets one electron from it, becomes atom of hydrogen and escapes our as hydrogen gas in the form of hobbles. Each of the negatively charged sulphate ion (SO₄^{- -}) reaching the anode gives two electrons to it, reacts with water ant forms suphuric acid and oxygen according to chemical reaction SO₄ + H₂O → H₂SO₄ + O. The oxygen produced attacks the lead anode and forms lead per oxide pbo2. Thus during charging lead cathode remains as lead but lead anode gets converted to lead per oxide (PbO₂), chocolate in colour.

Now if the cell is disconnected from d.c. source of supply and voltmeter is connected between the electrodes, it will show potential difference between them and on connecting these electrodes by a wire, current will flow form positive plate to the negative plate through external circuit, i.e. the cell is now capable of supplying electrical energy.

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