Which item is typically absent from both cars of a married pair?

The item that is typically absent from both cars of a married pair is the storage battery. In a married pair of rail cars, such as those coupled together for passenger service, electrical systems are often designed to be interconnected. Therefore, they typically share components like the electric brake circuit and the compressed air system, allowing for efficient operation and maintenance.

A storage battery is more commonly found in individual cars, where it serves to power systems independently in case of an electrical failure or when the train is not connected to an external power supply. In a married pair, these cars rely more on shared electrical systems and do not each carry a separate storage battery, leading to an optimized design and weight distribution. This design choice minimizes redundancy and potential points of failure in the electrical systems of the paired cars.