An implantable device comprises a reservoir that contains a fluid for filling an inflatable portion of a gastric band. A device is coupled to the reservoir and includes stored potential energy having a first state and a second state. The first state represents a higher level of potential energy and the second state represents a lower level of potential energy. The implantable device further comprises a filling valve coupled between the reservoir and the gastric band, and the filling valve is configured to be opened in response to a first telemetric signal. The stored potential energy decreases from the first state to the second state when the filling valve is open, and a filling amount of the fluid moves from the reservoir to the gastric band when the stored potential energy decreases from the first state to the second state.
