Patent ID: 8159228

Claim:
A method of determining internal resistance of a vehicle battery used to power one or more vehicle loads, the method comprising: periodically sampling current and voltage outputted from the battery to determine sampled current and voltage values; filtering the sampled current and voltage values into switching events, each switching event including at least one sampled current value, defined as a peak current value, that is greater than a current threshold; determining an internal resistance value for each of the switching events by averaging a division of the voltage value by the current value sampled at the same time for each voltage value and current value corresponding with each of the peak current values; weighting a ‘q’ number of the internal resistance values; determining the internal resistance to be an average of the weighted internal resistance values; and arranging the sampled current and voltage values into the same switching event if the sampled current and voltage values occur between a beginning and ending defined for each switching event, the beginning corresponding with the first sampled current value above the current threshold and the ending corresponding with the first successive sampled current value below the current threshold.