What does the BATT IN USE light indicate when it is illuminated?

The illumination of the BATT IN USE light signifies that something is being energized from the aircraft's battery. This indicates that the battery is supplying power to the aircraft's systems, which may occur during operations where external power is unavailable or when the aircraft is in a state where the primary power sources are not engaged.

In the context of aircraft systems monitoring, this light serves as a critical alert for pilots and crew, informing them that the battery is actively providing electrical power, which necessitates monitoring the battery's condition and charge status. This includes understanding that while it may imply that the battery is in use, it does not directly correlate with the battery being fully charged, imminent battery depletion, or that all systems are functioning normally. Each of those situations requires further investigation or has other indicators associated with them. The BATT IN USE light is specifically related to the active usage of battery power.