Proper understanding of heat generation and design of heat dissipation paths are critical for ensuring the safety of lithium ion modules during abuse events such as external shorts. Additionally, the behavior of positive thermal coefficient (PTC) current limiting devices—generally effective at the single-cell level—can be difficult to predict for a multi-cell module. To help guide battery pack design, a coupled thermal/electrical model of a commercial 18 650-size cell and a module with 16 cells in parallel (16P) are developed. Cell electrical response is modeled using an equivalent circuit, including the temperature-dependent behavior of the PTC. Cell thermal response is modeled with a high-resolution thermal model from which a simpler 5-node thermal circuit model is extracted. Cell models are integrated into a module-level model considering cell-to-cell electrical and thermal interactions via conduction, convection, and radiation. The module-level model is validated with a 16P external short experiment and applied in a parametric study to assess thermal safety margin. Copyright © 2009 John Wiley & Sons, Ltd.