An electrical charging system configured to wirelessly charge an energy storage device, such as a battery. The charging system includes an off-transducer in electrical communication with an alternating power source and electromagnetically coupled to an on-vehicle transducer connected to the energy storage device. A controller adjusts a variable frequency oscillator within the power transmitter, thereby changing the frequency of the sourced electrical power. The charging system further includes a phase detection circuit in communication with the controller and the off-transducer and configured to determine a phase difference between the alternating voltage and the alternating current supplied by the power source. The controller is configured to adjust the variable frequency oscillator based on the phase difference such that the frequency of the sourced electrical power maintains the phase difference within a desired range.