The Electronic Speed Control (ESC) has an embedded "auto-cutoff" controller that will reduce battery power supplied to the motor as the battery reserve begins to run out. This auto-cutoff controller ensures that the battery retains sufficient energy to power the receiver and servos. As the energy reserve in the battery approaches "empty", the auto-cutoff begin to reduce power available for the motor while allocating the remaining energy to provide power for the receiver and servos so that you can maintain flight control using the remaining energy.

 

Land immediately when you detect that the motor power is beginning to fade. Once the power begins to fade, you have a very short time remaining before the ESC will auto-cutoff power to the motor.