A monitoring system for a battery system includes a battery system including a battery pack. The battery pack includes M battery modules, where M is an integer greater than zero. Each of the M battery modules includes C battery cells, where C is an integer greater than one. T temperature sensors configured to generate sensed temperatures of the M battery modules, where T is greater than or equal to M and less than M times C. A battery management module configured to perform battery impedance measurements on the C battery cells of the M battery modules; generate estimated temperatures for each of the C battery cells of the M battery modules based on the battery impedance measurements; and selectively detect at least one of the C battery cells having a cell outlier temperature based on the estimated temperatures of the C battery cells.