Final answer:
The question pertains to the auxiliary power system in a metro rail, likely the batteries, which are not the main source of propulsion power as metro systems primarily use wired systems such as overhead lines or third rails.
Step-by-step explanation:
The question suggests it relates to the specifics of an electric propulsion system used in a metro rail system. The batteries mentioned are likely part of an auxiliary power system since main propulsion for metro rails typically uses wired systems. Metro rails draw electricity either from overhead lines or a third rail to provide the power needed for operation. These systems can supply higher voltages necessary for efficient transportation, as is evident with high-speed trains and light rail systems that utilize these methods for electrical power.
Light-rail trains could use batteries for backup power or for onboard systems that require direct current (DC). When the question states that the batteries provide 37.5 VDC, it implies that they are not the primary source for propulsion, which requires much higher voltage levels. A light-rail commuter train, for example, draws 630 A of 650-V DC electricity when accelerating. This example demonstrates the substantial power requirements of such transit systems, as opposed to the significantly lower voltage provided by the batteries under discussion.