A new model for a lead-acid battery pack is proposed for use in power simulations of electric vehicles. A linear approximation using a constant voltage drop has been used to model the charge-transfer resistance of the battery pack, and an exponential voltage-recovery equation has been used to model the transient capacitance effects following a period of discharge. The new model is easy to implement with simple calculations and easily acquired parameters, combining speed of implementation with accuracy. The new model was found to have a peak error of 3.1% in drive cycle tests, thus comparing favorably to existing models of similar complexity. An initial assessment of the model's suitability for use with a lithium-ion battery pack was also performed, finding a peak error of 5%.