The invention relates to methods and apparatus to measure route resistance of a battery system. A technical problem that the invention solves is improving battery operation and providing more accuratebattery data. The method and apparatus may comprise utilizing various parameters, such as known resistance characteristics, voltage, and current to calculate the route resistance of the battery. In various embodiments, the route resistance may be used to provide a more accurate estimate of the relative state of charge (RSOC). A technical effect realized by the invention is improved battery operation and more accurate battery data.