To anticipate accurate charging time by providing a battery capacity detecting means of a secondary battery and a charging current detecting means, providing a battery pack having a charging current detected by the charging current detecting means and residual charging time data corresponding to capacity of the battery capacity detecting means, and determining residual charging time.

Electronic equipment is desirably provided with a battery capacity detecting means of a secondary battery and a charging current receiving means for receiving a charging current from a device main body or an expander, and is provided with charging current data received by the charging current receiving means of a battery pack and residual charging time data corresponding to capacity of the battery capacity detecting means to determine residual charging time. The battery pack is desirably provided with a means for transmitting residual charging time information determined by a residual charging time calculating means to the device main body or the expander, the device main body or the expander is provided with a charging current detecting means, and is provided with a means for transmitting the charging current to the battery pack to transmit predetermined plural fixed charging current values to the battery pack.