NOVELTY - Secondary battery system comprises first and second temperature measurement units that measure temperature in central area (2) and in outer circumferential area (4) of core winding (1); temperature difference calculation unit that calculates temperature difference ( delta T) at core winding; change quantity calculation unit that calculates change quantity ( delta TT) indicating extent of change in temperature difference ( delta T); and heat generation distribution detection unit that executes detection of heat generation distribution at winding assembly based on change quantity ( delta TT).    USE - Secondary battery system used for controlling charge/discharge of secondary battery used in hybrid vehicle, electric vehicle or hybrid railway vehicle or in industrial storage battery used for purposes of electricity storage.    ADVANTAGE - The secondary battery system detects abnormality in heat generation distribution at earlier stage by ascertaining any change occurring in cell, thus making it possible to detect fault quicker than any of current heat generation quantity detections while executing battery operational control and battery maintenance and management with higher level of reliability.    DETAILED DESCRIPTION - Secondary battery system comprises first temperature measurement unit that measures temperature in central area (2) of core winding (1); second temperature measurement unit that measures temperature in outer circumferential area (4) of core winding; temperature difference calculation unit that calculates temperature difference ( delta T) between temperature in central area and temperature in outer circumferential area at core winding, respectively measured by first temperature measurement unit and second temperature measurement unit; change quantity calculation unit that calculates change quantity ( delta TT) indicating extent of change in temperature difference ( delta T) between temperatures in central area and in outer circumferential area of core winding represented by difference between temperature difference ( delta T1) calculated at start of use of secondary battery and temperature difference ( delta T) calculated after predetermined length of time elapses following start of use of secondary battery; and heat generation distribution detection unit that executes detection of heat generation distribution at winding assembly based on change quantity ( delta TT). The heat generation distribution detection unit determines that heat generation density is higher toward outer circumferential side beyond middle area of winding assembly on radial direction when change quantity is less than first threshold value; or determines that heat generation density is higher toward center beyond middle area of winding assembly on radial direction if change quantity is greater than second threshold value; or determines that heat generation density is evenly distributed or that heat generation density is high at winding assembly in middle area on radial direction if change quantity is equal to or greater than first threshold value and equal to or less than second threshold value. The secondary battery system also comprises third temperature measurement unit that measures temperature in surrounding area around secondary battery.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of cylindrical battery core winding of secondary battery system.    Core winding (1)    Central area (2)    Inner portion (3)    Outer circumferential area (4)    Heat flow (5)    Temperature distribution (40)