the lithium ion battery and the environment of the lithium ion battery module 41 while the power switching device 43 may include for example a semiconductor switch a mechanical switch an inverter or a dc dc converter as power conversion equipment etc the power switching device 43 are not limited thereto and any of devices capable of controlling the current value upon charging and discharging to the lithium ion battery module 41 may be used the power conversion device 51 is a device which converts a dc current obtained from the lithium ion battery into an ac current in response to the load usually an inverter is preferably used as the power conversion device 51 a capacitor 52 is connected in parallel with the power conversion device 51 even if power supply to the power conversion device 51 is reduced to 0 instantaneously current is discharged from the capacitor 52 thereby allowing stable power to be supplied to the power converter 51 the electric load 71 may be a heater an electric brake an electric power steering or an electric motor for example in the use to an automobile then the charge discharge control method by the control device 61 will be described fig3 is a flow chart of a secondary battery system according to this embodiment first at the starting step s 001 an instruction for starting charging to the lithium ion battery module 41 is sent as a signal.