What is the minimum battery voltage below which external power should not be connected?

The correct answer is that external power should not be connected when the battery voltage falls below 22.0 V. This minimum voltage is critical for several reasons. First, if external power is connected when the battery is too low, it can lead to inadequate charging or potentially damage the battery and the electrical systems of the aircraft. A battery that is below this threshold may not support the necessary loads during the transition to external power or may not react appropriately during the charging process.

Connecting external power at voltages lower than 22.0 V may also result in unstable power supply, which can negatively affect the aircraft’s avionics and systems that rely on a steady and sufficient voltage. By ensuring the battery maintains a voltage above this minimum threshold, the integrity of the battery and associated systems can be preserved, thereby maintaining operational safety and reliability.