What is the primary use of power from the storage batteries in trains?

The primary use of power from storage batteries in trains is indeed to operate emergency lights. Storage batteries provide a reliable source of electricity independent of the train's main power system, ensuring that emergency lights function during instances of power failure or when the train is not receiving power from an external source.

In the event of a power outage or when the engine is not operational, these batteries ensure that safety features like emergency lighting remain active, helping to guide passengers safely and ensuring visibility for conductors and crew during emergencies.

Other functions of storage batteries, while important, do not represent their primary purpose. For example, activating the train horn, charging the air compressor motors, or powering the main engine are secondary or auxiliary uses and typically depend on different systems or power sources within the train's electrical architecture. Thus, the effective operation of emergency lighting is crucial for safety, making it the main use of power from storage batteries.