A series-type charging and discharging apparatus without current interruption comprising: a bi-direcitonal main charging and discharging power supply for series-type charging and discharging without current interruption; a plurality of secondary batteries connected in series to be charged and discharged using said bi-directional main charging and discharging power supply continuously according to a predetermined recipe without interruption, and a plurality of auxiliary charging power supplies each of them installed in parallel to a respective different battery of the plurality of individual batteries connected in series to compensate for a capacity difference between a plurality of secondary batteries connected in series, wherein each of the auxiliary charging power supplies is configured as an insulated unidirectional switch mode DC-to-DC converter configured to use a power source of a DC grid, which is an input terminal of the main charging and discharging power supply, a separate DC power as an electrical input or to use power to be extracted from a separate AC power, and to use a voltage of the respective individual battery as an output to compensate for a capacity difference between a plurality of secondary batteries connected in series, wherein each of the auxiliary charging power supplies is configured to perform a function of supplementing a charging current for batteries with a capacity larger than the capacity of the battery with the smallest capacity in a charging process of the plurality of secondary batteries connected in series and to perform a function of supplementing a discharging current for batteries with a capacity smaller than the capacity of the battery with the largest capacity in a discharging process of the plurality of secondary batteries connected in series. a bi-direcitonal main charging and discharging power supply for series-type charging and discharging without current interruption; a plurality of secondary batteries connected in series to be charged and discharged using said bi-directional main charging and discharging power supply continuously according to a predetermined recipe without interruption, and a plurality of auxiliary charging power supplies each of them installed in parallel to a respective different battery of the plurality of individual batteries connected in series to compensate for a capacity difference between a plurality of secondary batteries connected in series, wherein each of the auxiliary charging power supplies is configured as an insulated unidirectional switch mode DC-to-DC converter configured to use a power source of a DC grid, which is an input terminal of the main charging and discharging power supply, a separate DC power as an electrical input or to use power to be extracted from a separate AC power, and to use a voltage of the respective individual battery as an output to compensate for a capacity difference between a plurality of secondary batteries connected in series, wherein each of the auxiliary charging power supplies is configured to perform a function of supplementing a charging current for batteries with a capacity larger than the capacity of the battery with the smallest capacity in a charging process of the plurality of secondary batteries connected in series and to perform a function of supplementing a discharging current for batteries with a capacity smaller than the capacity of the battery with the largest capacity in a discharging process of the plurality of secondary batteries connected in series.