The present invention is disclosed herein as an electrochemical cell having a cell housing with a first half cell and a second half cell, and an ion selective membrane between the cells. The electrochemical cell further has a first electrode positioned within the first half cell, a second electrode positioned within the second half cell, an electrolyte in electrical communication with both the first electrode and the second electrode. The electrodes of the cell are configured so that the electrochemical cell maintains a substantially constant salt concentration level throughout operation. The cell is preferably used in conjunction with an implantable fluid delivery apparatus. A method for using the device is additionally disclosed.