What indicates a malfunction on a GMDSS station with a 24 VDC battery system?

A constant 30 volt reading on the GMDSS console voltmeter indicates a malfunction because the expected normal operating voltage for a 24 VDC battery system should generally be around 24 volts, with potential fluctuations due to charging or load conditions. A reading that remains consistently at 30 volts suggests that something abnormal is happening, such as overcharging or a fault in the voltage monitoring system, which can potentially damage the equipment or lead to system failures.

In contrast, the other choices describe scenarios that are either within normal operational variations or do not effectively indicate a malfunction. For instance, a high rate of charge that declines after testing could simply reflect normal battery charging behavior, while a voltmeter reading that fluctuates indicates the battery and monitoring system are responding to demands rather than malfunctioning. Thus, the consistent overvoltage reading is the clear indicator of an issue.