When should you use a Ground Power Unit (GPU)?

Using a Ground Power Unit (GPU) when battery volts are between 20V and 24V is advisable to ensure optimal performance and safety of the aircraft's electrical systems. When the battery voltage falls below this range, the electrical output may be insufficient to power the aircraft's systems effectively, potentially leading to operational issues during startup or before takeoff.

In this situation, connecting a GPU helps to provide a stable power source, allowing for a smoother start and reducing the strain on the aircraft's batteries. This practice also helps in maintaining battery health by preventing excessive discharging, which can occur if the aircraft relies solely on the battery at lower voltages. Keeping the voltage within the specified range ensures that all systems can operate as intended, minimizing the risk of failure or malfunction during critical phases of flight preparation.