Alkali metal thermal-to-electric converter (AMTEC) technology is ideally suited for a wide range of applications from space, aerospace and military to domestic and other terrestrial civilian applications. In spite of its many advantages, existing AMTEC technology has some drawbacks that prevent the realization of the full potential of the technology. The problem is that the cell efficiency is still below its theoretically achievable value, and the cell has an adverse power-time characteristic. The maximum power output of the cell was observed to decrease from 2.54 W at the end of 172 h to 1.27 W during its 18,000 h of cell operation. This problem may preclude the use of the cell for applications that require operation of the cell for long periods of time. This paper deals with the factors responsible for this degradation and discusses in detail the simulation model used to study and predict the performance of the cell as a function of time. It is shown that the p-alumina solid electrolyte is a major cause of this degradation and a model to simulate its performance is developed and compared with available experimental data to establish the role of the electrolyte.