NOVELTY - The method involves detecting battery temperature, and detecting battery voltage and current at the detected temperature. Internal resistance is computed from the voltage and the current. Battery internal resistance versus measured temperature relation is established using the internal resistance computed from actual measurements to determine internal resistance at a set of battery temperatures, where actual measured internal resistance and relation between the internal resistance and a degree of degradation data indicating the degree of battery degradation.    USE - Method for detecting internal resistance in a high output battery i.e. power storage battery, that is installed on-board of a vehicle i.e. hybrid vehicle, to supply power to a motor that drives the vehicle and used for a power source system in home or manufacturing facility. Can also be used for a streetlight power source that is charged during a day by solar power and discharged at night and a backup power source to operate traffic signals during power outage.    ADVANTAGE - The method enables detecting the battery temperature and the internal resistance and computing the internal resistance at each temperature in an effective manner. The method enables utilizing actual measured battery internal resistance at a set of temperatures to detect the internal resistance, so that the internal resistance can be detected accurately over a wide range of temperatures. The method enables detecting the internal resistance to have characteristic that a degree of battery degradation can be accurately determined for battery operation over the wide range of temperatures. The method enables setting maximum current for battery charging and discharging from the temperature, the internal resistance and battery voltage, so that the battery can be discharged with large allowable current, thus minimizing battery degradation. The method enables protecting the battery during discharging even when the internal resistance is not been detected for long time period at current battery temperature. The method enables computing the internal resistance from a set of detection points and detecting the internal resistance in a high current region, thus computing the internal resistance in an accurate manner.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart illustrating battery internal resistance computation by a decision circuit.