Systems and methods for improved power transmission are disclosed herein. The system can include an implantable neurostimulator for delivering the one or more electrical pulses to a patient's body. The implantable neurostimulator can include a hermetic housing made of a biocompatible material, an energy storage feature for powering the implantable neurostimulator, a receiving coil assembly including an elongate wire winding wound around a first ferritic core, and control circuitry for controlling recharging of the energy storage feature. The system can include a charging device for wirelessly delivering energy to the implantable neurostimulator. The charging device can include a sending coil assembly including a planar wire winding coupled to a surface of a second ferritic core.