The present disclosure relates to a battery assisting apparatus and method for a fuel cell vehicle. An exemplary embodiment of the present disclosure provides a battery assisting apparatus for a fuel cell vehicle, including: a controller configured to determine an increase or decrease of driver's determination to accelerate based on a change rate of motor torque and a change rate of accelerator opening when a battery assistance mode is entered, and to release the battery assistance mode when the driver's determination to accelerate is decreased; and a storage configured to store data and algorithms driven by the controller.