This article focuses on developing a finite-element method (FEM) model for large capacitors’ thermal modeling and reliability analysis. Thermal modeling for capacitors is critical since the capacitor’s lifetime depends on the capacitor’s maximum temperature. Typically, capacitors have been modeled as a solid element, not considering the capacitor’s internal geometry, leading to temperature estimation errors and requiring extensive testing to adjust the model. The presented methodology to develop the model considers the internal geometry to obtain a reliable model, with sufficient simplicity to adapt the methodology to any electrolytic capacitor. To achieve good results, the capacitor’s winding is modeled as an anisotropic material to reproduce appropriately the behavior of the layers of aluminum and paper soaked in electrolyte. The results of the simulations match the experimental results closely, therefore validating the utility of the model.