A battery control system for a vehicle including a vehicle body , an engine and a motor installed on the vehicle body , and a secondary battery used as a driving power source of the motor , said battery control system being adapted to control the external charging unit, and comprising a degradation detecting unit that detects degradation of the secondary battery during external charging of the second battery by the external charging unit; a state-of-charge detecting unit that detects a plurality of specified states of charge ( SC1, SC2, SC3 ) of the secondary battery, the specified states of charge having different values from each other; and a degradation detection executing unit that causes the degradation detecting unit to execute a process of detecting degradation of the secondary battery in the specified states of charge ( SC1, SC2, SC3 ) while the external charging unit ( M1 ) externally charges the secondary battery, using the external power supply, characterized in that the vehicle includes an external charging unit ( M1 ) that externally charges the secondary battery, using an external power supply located outside the vehicle body, wherein the degradation detecting unit detects degradation of the secondary battery, based on magnitudes of battery resistances ( RAX, RAY, RAZ ) of the secondary battery in the specified states of charge ( SC1, SC2, SC3 ), the magnitudes of battery resistances (RAX, RAY, RAZ) being different from each other, the degradation detecting unit calculates respective state resistance change rates ( RMX, RMY, RMZ ) in the specified states of charge ( SC1 , SC2, SC3 ), based on the magnitudes of battery resistances ( RAX, RAY, RAZ ), the state resistance change rates ( RMX, RMY, RMZ ) being different from each other, and the degradation unit calculates an average resistance change rate ( RM ) of the state resistance change rates ( RMX, RMY, RMZ ) as indicators that indicate a degree of the degradation of the secondary battery. a degradation detecting unit that detects degradation of the secondary battery during external charging of the second battery by the external charging unit; a state-of-charge detecting unit that detects a plurality of specified states of charge ( SC1, SC2, SC3 ) of the secondary battery, the specified states of charge having different values from each other; and a degradation detection executing unit that causes the degradation detecting unit to execute a process of detecting degradation of the secondary battery in the specified states of charge ( SC1, SC2, SC3 ) while the external charging unit ( M1 ) externally charges the secondary battery, using the external power supply, characterized in that the vehicle includes an external charging unit ( M1 ) that externally charges the secondary battery, using an external power supply located outside the vehicle body, wherein the degradation detecting unit detects degradation of the secondary battery, based on magnitudes of battery resistances ( RAX, RAY, RAZ ) of the secondary battery in the specified states of charge ( SC1, SC2, SC3 ), the magnitudes of battery resistances (RAX, RAY, RAZ) being different from each other, the degradation detecting unit calculates respective state resistance change rates ( RMX, RMY, RMZ ) in the specified states of charge ( SC1 , SC2, SC3 ), based on the magnitudes of battery resistances ( RAX, RAY, RAZ ), the state resistance change rates ( RMX, RMY, RMZ ) being different from each other, and the degradation unit calculates an average resistance change rate ( RM ) of the state resistance change rates ( RMX, RMY, RMZ ) as indicators that indicate a degree of the degradation of the secondary battery. <EOS>