An external power supply system for an aircraft, comprising: a power receptacle configured to connect to an external power cable from an external power source to provide an external power; a manual control switch operative to switch between a battery power source and the external power source ; a voltage check system configured to prevent both under-voltage and over-voltage, the voltage check system including: a voltage relay sensor configured to determine if the external power is within a suitable voltage range, wherein the voltage relay sensor is configured to determine if the voltage of the external power source is within a low voltage threshold and a high voltage threshold; and a check switch , wherein if the external power is within the suitable voltage range, the voltage relay sensor is configured to activate the check switch to allow the external power to be output, and wherein if the external power is outside the suitable voltage range, the voltage relay sensor is configured to not allow power to be output; and at least one first indicator operatively connected to the power receptacle to indicate that the external power is available; wherein the voltage check system is configured to only allow activation of the at least one first indicator when the external power is within the suitable voltage range. a power receptacle configured to connect to an external power cable from an external power source to provide an external power; a manual control switch operative to switch between a battery power source and the external power source ; a voltage check system configured to prevent both under-voltage and over-voltage, the voltage check system including: a voltage relay sensor configured to determine if the external power is within a suitable voltage range, wherein the voltage relay sensor is configured to determine if the voltage of the external power source is within a low voltage threshold and a high voltage threshold; and a check switch , wherein if the external power is within the suitable voltage range, the voltage relay sensor is configured to activate the check switch to allow the external power to be output, and wherein if the external power is outside the suitable voltage range, the voltage relay sensor is configured to not allow power to be output; and at least one first indicator operatively connected to the power receptacle to indicate that the external power is available; wherein the voltage check system is configured to only allow activation of the at least one first indicator when the external power is within the suitable voltage range. a voltage relay sensor configured to determine if the external power is within a suitable voltage range, wherein the voltage relay sensor is configured to determine if the voltage of the external power source is within a low voltage threshold and a high voltage threshold; and a check switch , wherein if the external power is within the suitable voltage range, the voltage relay sensor is configured to activate the check switch to allow the external power to be output, and wherein if the external power is outside the suitable voltage range, the voltage relay sensor is configured to not allow power to be output; and at least one first indicator operatively connected to the power receptacle to indicate that the external power is available; wherein the voltage check system is configured to only allow activation of the at least one first indicator when the external power is within the suitable voltage range. <EOS>