In this paper it is analyzed the behavior of a battery/Superconducting Magnetic Energy Storage (SMES) hybrid Energy Storage Systems that can be used in a Fuel Cell/Renewable Energy Sources (RESs)/Hybrid Power System under an unknown load profile and variable RES power, which uses the Fuel Cell System as Auxiliary Energy Source. In general, the load demand profile includes large and sharp pulses, especially requested for space and military equipment, communication, and high-tech applications. The sizing and control of the battery/SMES Hybrid Power System under pulsed load are validated by simulations. The variability of the load demand and RES power is mitigated by using the Load-Following control for Auxiliary Energy Source of the RES Hybrid Power System. Thus, if the load power is higher than the RES power, then the battery will operate in charge-sustaining mode due to using the Load-Following control for Auxiliary Energy Source. Otherwise, the battery will operate in charge-increasing mode if the Hybrid Power System does not use an electrolyzer to be supplied with this excess of power. So, a reduced capacity is needed for battery operating in charge-sustaining mode due to use of the Load-Following control. However, the load pulses with large and sharp profile must be mitigated by the appropriate control of the SMES in order to protect the Fuel Cell system. So, the capacity of the SMES to generate (or to absorb) such pulses is analyzed in this paper. The simulation results illustrate the capacity of the SMES to generate different shapes of pulses. Thus, an effective mitigation of the load pulses is proposed here by controlling the SMES converter. Also, the design of the battery/SMES Hybrid Power System under dynamic load is presented.