In this paper, a simple transformation of coordinates is proposed that facilitates the efficient simulation of the non-isothermal lithium-ion pseudo 2-D battery model. The transformed model is then conveniently discretized using orthogonal collocation with the collocation points in the spatial direction. The resulting system of differential algebraic equations (DAEs) is solved using efficient adaptive solvers in time. A series of mathematical operations are performed to reformulate the model to enhance computational efficiency and programming convenience while maintaining accuracy even when non-linear or temperature dependent parameters are used. The transformed coordinate allows for efficient simulation and extension from cell sandwich to stack models. Furthermore, the transformation and reformulation techniques are used to simulate operation of an 8-cell battery stack subject to varying heat transfer coefficients as well as specified temperature boundary conditions. Mathematical modeling and simulation of the operation of lithiumion batteries is not trivial, as concentration and potential fields must be evaluated simultaneously in both solid and liquid phases. This is complicated by the fact that the transport and kinetic parameters which determine battery behavior are highly nonlinear, leading to very complex governing equations. Doyle et al. 1 developed a general model based on concentrated solution theory to describe the internal behavior of a lithium-ion sandwich consisting of positive and negative porous electrodes, a separator, and current collectors. 2 This model proved generic enough to incorporate further advancements in battery systems understanding, leading to the development of a number of similar models. 3-13 Reviews of models for lithium-ion batteries can be found elsewhere in the literature. [10][11][12] Table I depicts a pseudo-twodimensional isothermal model for a lithium-ion battery. 14-16 Table II presents the various expressions used in the model, while Table III shows the physical parameters used in this paper. For analysis and control of lithium-ion batteries in hybrid environments (e.g. with a fuel cell, capacitor, or other electrical components), there is a need to simulate state of charge, state of health, and other parameters of lithium-ion batteries in milliseconds. Full-order physics-based models may simulate discharge curves in several seconds to minutes, depending on the solvers, routines, computers, etc. In contrast, empirical models (based on correlations of past data) can simulate specific operating scenarios in milliseconds. However, use of these models under a different operating condition than for which they were developed may cause abuse or underutilization of electrochemical power sources. This paper presents a coordinate transformation and mathematical analysis for reformulation of physics-based models to solve them quickly, conveniently, and accurately in a way that is valid for a wide range of operating conditions and parameters. The porous electrode model as given in Ta...