A power system where energy generated at a deceleration time of a running vehicle such as an automobile can be accepted as regenerative energy sufficiently and safely is provided. In a power system 10, a non-aqueous solution system secondary battery group 1 where 10 to 11 lithium ion secondary battery cells are connected in series and an aqueous solution system secondary battery group 2 where 18 control valve type lead-acid battery cells are connected in series are connected in parallel. The battery capacity of the non-aqueous solution system secondary battery group 1 is smaller than that of the aqueous solution system secondary battery group 2. The non-aqueous solution system secondary battery group 1 and the aqueous solution system secondary battery group 2 are charged at a current value of 7C or less from a motor generator 3, and the ratio of the charged current value of the aqueous solution system secondary battery group 2 to the charged current value of the non-aqueous solution system secondary battery group 1 is 0.05 to 1.00.