A system adapted to calculate a battery usable time period of a mobile station when the system is arranged separately from the mobile station, the system comprising: a retrieval unit adapted to access an internal storing unit of the mobile station and to retrieve information regarding usage conditions including operating time periods, wherein the operating time periods indicate extents of utilizing a corresponding plurality of functions of the mobile station by a user; a storing unit adapted to store, for each of operating modes of the mobile station, average consumed current values for the corresponding plurality of functions; a calculating unit adapted to calculate, for each of the operating modes of the mobile station, the battery usable time period by calculating an added value, the added value being obtained by adding a product of the average consumed current value for one function of the plurality of functions and the operating time period of the one function of the plurality of functions over the plurality of functions, and by dividing a capacity value of a battery of the mobile station by the added value; and a display unit adapted to display the battery usable time periods of the mobile station to the user, wherein the retrieval unit is adapted to receive an input by the user, wherein the input is for selecting a plurality of mobile stations, wherein the storing unit is adapted to store the average consumed current value for each of the operating modes of each of the plurality of the mobile stations, wherein the calculating unit is adapted to calculate the battery usable time period for each of the operating modes of each of the plurality of the mobile stations, and wherein the display unit is adapted to display the battery usable time period for each of the operating modes of each of the plurality of the mobile stations. a retrieval unit adapted to access an internal storing unit of the mobile station and to retrieve information regarding usage conditions including operating time periods, wherein the operating time periods indicate extents of utilizing a corresponding plurality of functions of the mobile station by a user; a storing unit adapted to store, for each of operating modes of the mobile station, average consumed current values for the corresponding plurality of functions; a calculating unit adapted to calculate, for each of the operating modes of the mobile station, the battery usable time period by calculating an added value, the added value being obtained by adding a product of the average consumed current value for one function of the plurality of functions and the operating time period of the one function of the plurality of functions over the plurality of functions, and by dividing a capacity value of a battery of the mobile station by the added value; and a display unit adapted to display the battery usable time periods of the mobile station to the user, wherein the retrieval unit is adapted to receive an input by the user, wherein the input is for selecting a plurality of mobile stations, wherein the storing unit is adapted to store the average consumed current value for each of the operating modes of each of the plurality of the mobile stations, wherein the calculating unit is adapted to calculate the battery usable time period for each of the operating modes of each of the plurality of the mobile stations, and wherein the display unit is adapted to display the battery usable time period for each of the operating modes of each of the plurality of the mobile stations.