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Methods of Charging the Sealed Lead-Acid Battery

For charging the sealed lead-acid battery, a well- matched charger should be used because the capacity or life of the battery is influenced by ambient temperature, charge voltage and other parameters.

Charging methods are dependent on battery applications, and the applications are roughly classified into main power application and stand-by/back-up power applications.

Classification by application

  • (1)

    Main power source (Cycle use)

  • (2)

    Stand-by power source (Trickle use)

  • (a)

    Standard charging (Normal charging)

  • (b)

    Rapid charging

  • (a)

    Trickle charging

  • (b)

    Float charging

(1) Main Power cycle use Cycle use is to use the battery by repeated charging and discharging in turn.

(a) Standard charging (Normal charging) For common applications of the battery, the constant voltage charge method is advantageous as it allows the battery to exert full performance.

  • Constant voltage charging method

This method is to charge the battery by applying a constant voltage between the terminals. When the battery is charged by applying a voltage of 2.45 V per cell (unit battery) at a room temperature of 20C to 25C, charging is complete when the charge current continues to be stable for three hours. Sealed lead-acid batteries can be overcharged without constant voltage control. When the battery is overcharged, the water in the electrolyte is decomposed by electrolysis to generate more oxygen gas than what can be absorbed by the negative electrode. The elec- trolyte is changed to oxygen gas and hydrogen gas, and lost from the battery system. As the quantity of electrolyte is reduced, the chemical reactions of charge and discharge become inefficient and hence the battery performance is severely deteriorated. Therefore, exact voltage control and proper charging time in constant voltage charging are essential for securing the expected life of the battery.

  • Constant-voltage and constant-current charging

method This method is to charge the battery by controlling the current at 0.4 CA and controlling the voltage at 2.45 V / per cell (unit battery) at a room temperature of 20C to 25C. Proper charging time is 6 to 12 hours depending on discharge rate.

Constant-voltage constant-current charge characteristics

Charge voltage and charge current

~ ~

  • 0




Charge voltage

Charge current



6 Time (hours)

Sealed Lead-Acid Handbook, Page 20

January 2000

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