Which of the following circuits does the battery charger supply power to?

The battery charger is designed to supply power to essential systems within a transportation or industrial vehicle. When analyzing the options, the most appropriate choice is the internal and external lighting circuits.

The internal and external lighting circuits are critical for ensuring visibility and safety in various operational scenarios. These circuits require a reliable power source, especially when the primary power supply is interrupted or when the vehicle is stationary. The battery charger ensures that these lighting systems remain operational by supplying the necessary electrical power, thus facilitating safety for the vehicle operators and preventing accidents.

Other options focus on specific systems that, while important, might not be the primary focus of the battery charger in terms of maintaining continuous and reliable power. Cab control circuits, safety systems, and communication systems may utilize power from the battery but may not necessarily rely on the battery charger for their operation in the same critical way that lighting circuits do. Therefore, the choice that encompasses the most comprehensive and vital functions of the battery system is indeed the internal and external lighting circuits.