An intelligent rechargeable battery pack having a battery management system for monitoring and controlling the charging and discharging of the battery pack is described. The battery management system includes primary and secondary protection circuits for monitoring the charging and discharging of the battery. Individual battery cells forming the battery pack are connected by a main bus to a connector for connection to a battery charger or a device to be powered, and the main bus may be interrupted by a switch controlled by the battery management system to prevent damage to the battery during charging or discharging of the battery.