Patent ID: 7446510

Claim:
A diagnosis method for state-of-health (SOH) of batteries comprising the steps of: providing data of discharge voltages and discharge currents of a battery unit; setting an acceptable value of a predetermined period of time for calculating variation rates of discharge voltage and current of the battery unit, and setting an acceptable range of the variation rate of discharge current for the battery unit; calculating the variation rates of discharge voltages and currents of the battery unit within the predetermined period of time by using the data of the discharge voltage and current; recording the data of discharge voltages and currents of the battery unit and variation rates thereof; comparing the data of discharge voltages of the battery unit and the variation rates thereof if the variation rates of discharge current are fallen within the acceptable range of variation rate of discharge current with selected reference data; and converting results of compared data of discharge voltages of the battery unit and the variation rates thereof into a SOH index.