SOC (state of charge) estimation provides critical information to system engineers and end users of consumer electronics to electric vehicles. The accuracy of model-based SOC estimation depends on the accuracy of the underlying model, including temperature effects that greatly influence cell dynamics. This paper uses a 7th order, linear, ESPM (electrolyte enhanced single particle model) as the basis for a Luenberger SOC observer for a lithium ion cell. Isothermal and non-isothermal simulations compare the SOC from a commercially-available finite volume code and the SOC estimate for a wide range of temperature (0 <= T <= 50 degrees C) and pulse C-rates (vertical bar I vertical bar <= 15C). Arrhenius relationships between the ESPM model parameters and the sensed temperature improve SOC estimation. At low temperature (T < 10 degrees C) and low C-rates, temperature measurement reduces the RMS (root-mean square) SOC estimation error by up to ten times. At high temperature T >= 40 degrees C and high C-rates (vertical bar I vertical bar <= 15C), temperature measurement decreases SOC estimation error by more than three times. (C) 2014 Elsevier Ltd. All rights reserved.