US Patent 9267997 Systems and methods to determine the condition of a battery

Systems and methods for determining the damage level of a battery are provided. An exemplary method includes measuring a terminal voltage of the battery over time while discharging the battery at a predetermined current; calculating a slope of a natural logarithm of a rate of change of a first voltage of the battery over time based on the terminal voltage of the battery; and comparing the calculated slope to a threshold slope that is based on measurements of a plurality of similar batteries with known conditions. The first voltage of the battery may correspond to a voltage across an RC component of an equivalent circuit model for the battery.