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| the capacity of the battery. When the specific gravity reaches 1.160, the electrolyte should be renewed. (Normal specific gravity for the alkaline battery is from 1.190 to 1.230.) |

| Cell Voltages... |

| The voltage of both the lead and alkaline cells is about 2 V in an open circuit, that is, when no current is flowing. In practice, however, cells connected in series-parallel are usually arranged in batteries in sufficient number to meet the service requirements of voltage and current. |

| Because of low internal resistance, the voltage of a battery will not drop appreciably when a current is taken off. Heavy currents, in the range of 100 to 200 amperes, may be drawn off for a short time, such as during the operation of a breaker. Smaller currents of 10 to 20 amperes may be drawn steadily. The voltage keeps up well during most of the discharge, dropping off only at the end. |

| The voltage of an alkaline cell falls more rapidly during discharge than that of a lead cell. Consequently, lead cells are better suited than alkaline cells for use where a constant terminal voltage is essential. Typical charge and discharge curves for both lead and alkaline cells are shown in Figs. 15-10A and 15-10B. |

| Charging of Batteries |

| Batteries are charged with direct current that is sent through them in a direction opposite to the discharge current. The positive terminal of the battery is connected to the positive terminal of the charging source, and the negative terminal of the battery to the negative terminal of the charging source. The voltage of the charging source must be higher than the battery voltage in order to force the current through the battery in the proper direction. |

| Lead batteries may be charged at any rate that does not cause gasing. When they are nearly discharged, the permissible charging rate can be considerably greater than when the charge is built up. For minimum charging time, this situation calls for a continual reduction of the charging rate as the charge progresses. When a battery is charged from an essentially constant voltage source, a resistance is placed in the charging circuit. Since the voltage drop in the resistance is greater when larger current flows and lesser when smaller currents flow, the voltage applied at the lead cells tends to follow the optimum charging rate. |

| Alkaline batteries can be charged at any rate that does not cause overheating. The temperature of the cells should not exceed 46°C or 115°F. Within this limitation, the battery can be charged at a constant rate. |

| The batteries float on their dc supply line, that is, they are per- |

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