long wires on the power input to an ECU can lead to excessive ripple voltage at the input, damage to the input caps. Too much inductance, the pulsed current driving the motor leads to the ripple. You'd be better off extending the wires from the motor to the ECU and moving the ECU closer to the battery. Either that, or add extra capacitance to the input of the speed control. Dig around in the high performance electric plane forum for more info.