Patent ID: 8779725

Claim:
A method for improved battery protection cutoff for a rechargeable battery, the method comprising: measuring battery current flow by a battery controller coupled to a current sensor, updating, by the battery controller, an estimated charge state based on the measured battery current flow, measuring, by the battery controller coupled to a battery monitor coupled to the battery, a battery voltage and a battery temperature, determining, by the battery controller, an estimated internal resistance for the battery from a set of predetermined relationships among charge state, battery temperature, and internal resistance, using the estimated charge state and the measured battery temperature, determining, by the battery controller, a sag voltage from the estimated internal resistance and measured battery current flow, determining, by the battery controller, a no load voltage estimate for the battery by adding the sag voltage to the measured battery voltage, determining, by the battery controller, that the no load voltage estimate is equal to or less than a threshold voltage, and signaling by the battery controller, that the threshold voltage has been reached.