a user machine provided with a system of a software battery is connected to a host machine for providing a battery through a communications line , and a specific battery in a user machine is charged . the user machine includes a program for communications with the host machine and a software battery management system . the host machine includes a program having a function of listing available batteries , and transmitting a specified battery . with such a configuration , a user can select any battery from among the batteries in the host machine through communications , and charge for his or her own machine .