Importance

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Abstract

The subject invention pertains to a method and apparatus for recalibrating and/or estimating a battery's state of charge (SOC). The subject invention is advantageous in situations where the battery infrequently, if ever, reaches a full charge and/or a full discharge. In a specific embodiment, the subject method and apparatus can utilize a battery's voltage and/or current, and/or changes in a battery's voltage and/or current with time, to recalibrate and/or estimate the battery's SOC. The method and apparatus of the subject invention can monitor various parameters relating to the condition of the battery in order to determine where on the open circuit voltage (OCV) versus SOC curve, the dOCV/dSOC versus SOC curve, and/or d.sup.2 OCV/dSOC.sup.2 versus SOC curve the curve the battery is and, in a specific embodiment, when the battery reaches inflection point of the OCV versus SOC curve. Alternatively, the second derivative of the curve can be monitored to determine when the battery is outside a certain region, such as the 30% to 70% SOC region. If desired, the variation of the OCV versus SOC curve with respect to temperature and/or battery age can be taken into account during the determination of SOC in order to enhance the accuracy of such SOC determination.

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First Claim