What does a deflection of zero in an ammeter indicate?

A deflection of zero in an ammeter signifies that there is no current flowing through the circuit being monitored. This indicates that the battery is in a state where it is neither charging nor discharging. In practical terms, when the ammeter shows a zero reading, it suggests that there is no electrical demand being placed on the battery or that the battery system is in a standby condition.

This zero deflection can occur when all systems connected to the battery are turned off, or when the battery is disconnected from the circuit. Consequently, it ensures that there is no power being used by the aircraft’s systems at that moment, establishing a baseline for evaluating the battery's health and operational status.

Other answers might imply specific states of electrical activity or problems with the alternator or battery, but a zero reading specifically reflects inaction in terms of current flow, which is precisely what option B indicates.