1. A method for estimating a parameter of a battery system, comprising: generating an initial plurality of particles, each particle representing at least one parameter and at least one state of a battery system; generating a tuned plurality of modeled particle values by performing an iterative process a plurality of times starting with the initial plurality of particles, the iterative process comprising: propagating each of the plurality of particles through a system model representing the battery system to obtain a first plurality of modeled particle values; assigning a weight to each of the plurality of modeled particle values based upon a comparison of the plurality of modeled particle values to at least one measurement of an electrical parameter of the battery system; generating a successive plurality of particles based upon the weight assigned to each of the plurality of modeled particle values; and repeating the iterative process using the successive plurality of particles; estimating at least one parameter of the battery system based on one or more of the tuned plurality of modeled particle values.