The present disclosure provides a charging method, device, and system. The charging device includes a voltage regulation circuit, and can charge a charged device through voltage step-down or voltage step-up. In addition, the charging device and a charged device can transfer statuses of a circuit and a battery through a change of a switch status, so that the charging device can regulate a charging voltage and/or a charging current based on the statuses of the circuit and the battery.

During parallel charging, a control device sets a minimum value of first allowable input power of a first battery and second allowable input power of a second battery as common requested power of the first and second batteries, sets total requested power based on the common requested power, requests charging equipment for the total requested power or a total requested current that is based on the total requested power, and controls first and second inverters using the common requested power or a current command for the second battery that is based on the common requested power. The control device requests the charging equipment to stop the parallel charging when a difference between the common requested power and charging power of the second battery or between the current command for the second battery and a charging current of the second battery is equal to or larger than a predetermined value.

In a management device that manages a parallel system for power storage where a plurality of series-connected cell groups are connected in parallel, controller (16) derives deviations of currents flowing through the plurality of series-connected cell groups, and calculates an upper limit value of a charging current or charging power of the whole parallel system or an upper limit value of a discharging current or discharging power of the whole parallel system based on the derived current deviations. Controller (16) adjusts the upper limit value by multiplying the upper limit value by a coefficient (01) in accordance with a condition at a time of deriving the current deviations.

A battery pack is provided in which the battery pack itself can recognize a determination of a full charge, which is made by a charger, without using a communication line. A battery pack is provided with a secondary battery, current measurement means for measuring a charging current for charging the secondary battery, and a control circuit which receives an output signal from the current measurement means. The control circuit determines that the secondary battery is fully charged when a reduction rate of the charging current in a unit time exceeds a predetermined value.