NOVELTY - A charge status detector detects charge status of the secondary battery charged by the fuel cell. A CPU maintains power generation in the fuel cell until a detection result from the detector is higher than a threshold value before stopping the power generation. It stops power generation in the fuel cell based on a power generation stopping command from a stop button if the detection result is lower than the threshold value and higher than a second threshold value. The CPU determines if the system is connected with an external power source and stops power generation if it is connected.    USE - For transportation equipment e.g. a motorbike (claimed). The fuel cell system is mounted on the transportation equipment or an electronic apparatus and generates electric energy for driving the electric motor and other system component. It is applicable to other transportation equipment, such as automobile, marine vessel, and other similar transportation equipment. The fuel cell system is also applicable to a hydrogen fuel cell system in which hydrogen gas is supplied as a fuel to the fuel cell, or to a fuel cell system using a reformer.    ADVANTAGE - Power generation in the fuel cell is controlled in response to the charge status detection result showing a value higher or lower than the threshold value representing the charge amount needed for the battery in the next system operation. This maintains operator convenience and assures that the system can transfer to its normal operation in the next operation. Power generation in the fuel cell is stopped when the system is connected with an external power source to prioritize charging of the external power source and reduce the fuel amount to be replenished, resulting in saved fuel. The fuel cell system assures a successful transfer to normal operation when the system is started the next time while maintaining operator convenience.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method of operating a fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart of an alternative operation method.