How a battery works
Conversion of chemical into electrical energy requires two electrodes (galvanic process); these electrodes are connected to one another within the cell through a solution (electrolyte). When in a charged state, the electrode plates consist of lead and lead dioxide. The positive electrode consists of lead dioxide, and the negative electrode of diffuse spongy lead. The sulphuric acid forms the electrolyte. It enables a flow of ions between the electrodes. The electrolyte, which consists of sulphuric acid and distilled water, can be in liquid or gel form, or it can be bound in a layer of fibres (sealant).
A lead battery, sometimes also known as a lead accumulator, is a so-called secondary element, in other words it forms part of a combination that can only output electrical energy that has been fed into it previously. A lead battery contains a combination of various substances that can absorb or discharge electrical energy by means of a reversible chemical reaction. With accumulators, the chemical reaction that delivers electrical energy is reversible. Once the reaction has ceased as the energy is output (battery discharging), fresh energy can be input from outside (charging with DC current), and the chemical system is restored to more or less its initial state.
When the battery supplies current, the negatively-charged sulphate ions (SO4 2-) from the sulphuric acid (H2SO4) attach themselves to the plates. This results in both plates gradually turning into lead sulphate (PbSO4). The uncharged lead atoms (Pb) in the lead plate receive a double positive charge (Pb 2 +), and the lead ions in the lead-dioxide plate, which previously had a quadruple positive charge (Pb 4+), follow suit and likewise take a double positive charge. The lead plate is electrochemically oxidised (from Pb to Pb 2+), and the lead-dioxide plate undergoes an electrochemical reduction (from Pb 4+ to Pb 2+). To balance out this drop in charge, electrons flow from the lead plate to the lead dioxide plate. The battery delivers current.