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| Figure 15-2 Methods of connecting cells: (A) Series, (B) multiple or parallel, and (C) series parallel. |

| called Edison battery or alkaline battery. It is more expensive than the lead battery but has certain advantages. |

| The open-circuit voltage of any storage cell depends almost entirely on its chemical constituents and to some extent on the strength of the electrolyte and its temperature. The terminal voltage of the cell rises when the cell is charged and falls when it is discharged. The voltage of the battery is the voltage of one cell multiplied by the number of cells connected in series. The cells may be connected in series, in multiple or parallel, or in series parallel (Fig. 15-2). |

| The capacity of a cell depends approximately on its plate area. Its discharge rate is given in terms of ampere-hours at a standard temperature of 25°C or 77°F. The capacities of all storage cells and batteries decrease as the rate of discharge increases. |

| Lead Storage Battery |

| The active material of the lead storage battery is lead peroxide (PbO2) on the positive plate and finely divided or sponge lead (Pb) on the negative plate. The electrolyte is a solution of sulphuric acid (H2SO4) and water (H2O). |

| Discharge |

| When a cell is being discharged (Fig. 15-3A), electric current is produced as the acid in the electrolyte gradually combines with the active material of the plates. The acid in the pores of both plates chemically combines with the active materials and changes them into lead sulphate. Water is also formed at the same time and further dilutes the electrolyte. As the discharge proceeds, additional acid is withdrawn from the electrolyte and the formation of lead sulphate and water continues under the influence of the discharge current. At the point of complete discharge (Fig. 15-3B), the acid in the electrolyte will be reduced to a minimum. It will thus be seen that the formation of lead sulphate is the normal function of discharge. |

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