A sensitivity analysis of a mathematical model of a lithium–sulfur (Li–S) battery was performed, focusing on the precipitation rate constants and sulfur content, by investigating the response of the model to the variation of these parameters over a wide mathematical range. The necessity of rapid dissolution of elemental sulfur and rapid precipitation of reduced sulfur is discussed in detail. The sensitivity analysis suggests modifying the reduction reaction steps of sulfur can improve the predictions of the model of Li–S battery. Furthermore, an upper limit on the sulfur content of the cathode exists to ensure optimal performance. Although the model provides valuable knowledge concerning Li–S batteries, a modification to the assumed five-step reduction of sulfur combined with the consideration of the insulating nature of the active material is required to improve the model.