Final answer:
The minimum battery voltage for an APU start using batteries is typically around 24 volts. When using a GPU, the minimum voltage required for an APU start can be lower, around 18 volts.
Step-by-step explanation:
The minimum battery voltage for an APU start using batteries or GPU respectively
The minimum battery voltage for an APU start using batteries is typically around 24 volts. This voltage allows the APU to generate enough power to start up and provide electrical power to the aircraft systems. On the other hand, when using a GPU (Ground Power Unit), the minimum voltage required for an APU start can be lower, around 18 volts. This is because the GPU is an external power source that can provide more power to the APU than the aircraft's batteries alone.