Abstract: Improved battery charge state determination. The estimated charge state of a battery comprising a plurality of series connected cells is updated using Coulomb counting during battery operation, for example, while operating an electric vehicle motor. The estimated charge state may be coupled to a fuel gauge. When the battery is in a no load state, a no load voltage measurement is made. During testing, a set of relationships between battery no load voltages and associated known good charge states have been determined. The measured no load voltage is compared to the set of no load voltages associated with known good charge states. A known good charge state associated with the measured no load voltage is used to update the estimated charge state, thereby providing a more accurate indication of the actual battery charge state, thus providing a more robust and accurate fuel gauge.

Abstract: An energy storage system having one or more battery packs and a system controller for controlling the battery packs. Each battery pack has rechargeable storage cells and a battery pack controller in communication with the system controller. Through the operation of the system controller, battery packs with different initial charge states can be operated in parallel during a charge process and a discharge process. Discharging multiple battery packs in parallel offers not only a higher capacity and a longer run time than is available from a single battery pack, but also offers higher peak currents than available from a single battery pack, which are important in motor control applications. A battery pack design including a battery pack connector with both power and control contacts supporting user replacement of the battery packs.