An external power source, implantable medical device, and method for indicating an extent of power transfer between an external coil to an internal coil associated with the implantable medical device. According to one aspect, a method includes determining a parameter that depends on an extent to which the external coil is aligned with the internal coil, where the parameter includes at least one of an indication of an internal coil output power and power transfer efficiency and a resonant frequency of the external coil when inductively coupled to the internal coil. The method further includes indicating an extent to which the external coil is aligned with the internal coil based on the parameter.