The polymer electrolyte in a research and development test cell has been optimised in terms of ionic conductivity, cell internal resistance (the polymer electrolyte has a direct effect on the interfacial independence), cell rate performance and first discharge performance. A standard cell configuration has been defined for operation at 120 C and used for all subsequent evaluation and testing. Particular emphasis was placed on the cell lamination technique which was found to be critical for good cell performance. The cells were found to tolerate moderate degrees of overdischarge but large amounts cause premature deterioration in the long term cycling performance. The effect of overcharge to 3.50 V is actually beneficial to the cell cycling performance, but overcharge to 3.75 V causes rapid cell failure due to electrolyte breakdown. Results indicate that a substantial degree of the capacity fade with cycling, found in previous programmes, can be explained by inadequate charging. Several methods of charging have been investigated and the optimum recommended method achieves excellent retention of capacity over the first 20-30 cycles. However no longer term cycle tests have been performed.