Hybrid-electric and pure electric vehicles include a traction battery comprised of many cells. Controlling a battery system may require that a battery state of charge and a battery capacity be known. The state of charge and battery capacity values may be derived from estimated traction battery model parameters. The accuracy of the estimated model parameters depends on the signal richness and convergence properties of the estimation scheme. Accurate model parameters may be estimated when a persistent excitation condition and an estimation convergence condition are met. If the conditions are not met, active excitation of the battery may be performed to improve the chances of meeting the conditions.