At what battery voltage should external power not be connected?

The appropriate battery voltage at which external power should not be connected is 22 volts. Connecting external power at this voltage level can potentially damage the aircraft's electrical systems or components. At 22 volts, the battery voltage is indicative of the battery being near or below its minimum operational threshold. It is essential to ensure that the battery maintains adequate voltage levels for safe operation and to prevent complications with the aircraft's electrical infrastructure.

Furthermore, higher voltage thresholds, such as 23.5 volts and 25 volts, indicate that the battery is in a healthier state, where connecting external power would typically be acceptable. Therefore, understanding the critical voltage levels is crucial for maintaining the integrity and functionality of the aircraft's battery and electrical systems.