Two types of battery chargers are available for switchgear control power. One is known as the trickle-charge, which is the unregulated type, and the other is the regulated type. The regulated charger provides longer life, especially for lead–acid batteries. The regulated charger is recommended for switchgear applications. The selection of charger equipment should satisfy the following functions simultaneously:
• Steady-state loads on the battery
• Self-discharge losses of the battery
• Equalizing charges
Steady-state loads are those that require power continuously. Self-discharge losses are due to trickle current, which starts at about 0.25% of the 8 h rate for lead–acid batteries. Self-discharge losses increase with the age of the battery. The equalizing charge is an extended normal charge and is given periodically to ensure that the cells are restored to the maximum specific gravity. All lead– acid batteries require a monthly equalizing charge except the lead–calcium type. Nickel–cadmium batteries do not require the equalizing charge; however, it is recommended for occasional boosting. In the sizing of charger equipment, the steady-state loads, equalizing-charge current, and self-discharge current should be added to arrive at the capacity of the charger. Select a charger with ratings that exceed or equal the sum of currents required.