Adjustable gastric band implants contain a hollow elastomeric balloon with fixed end points encircling a patient's stomach just inferior to the esophago-gastric junction. These balloons can expand and contract through the introduction of saline solution into the balloon. In current bands, this saline solution must be injected into a subcutaneous port with a needle to reach the port located below the skin surface. The port communicates hydraulically with the band via a catheter. As an alternative to using a percutaneously accessed injection port, a system for regulating the flow of saline that is totally implanted may rely upon bi-directionally pumping fluid from an implant device. This system instead transfers AC magnetic flux energy from an external primary coil to a secondary coil that powers the pump in the implanted reservoir. A magnetically permeable rod centered within the primary coil increases power coupled to the secondary coil.