A plurality of charging devices 30 may be connected to a computer 10, 110 via a network 60. When computer 10 receives chewing information from a charging device 30 before performing a charging operation, computer 10 may compute the optimal charging period based upon the charging information. Parameters defining the optimal charging period may be transmitted to the respective charging devices 30. Each charging device 30 may perform the battery charging operation based upon the transmitted parameters. Thus, a network system can manage and control the charging operations for the plurality of charging devices in order to optimize charging period, optimize the number of charging devices 30 and battery packs 50 in use and maximize battery life.