This work aims at the development of a simulation tool to optimize the design of a hybrid fuel cell/battery system to supply ICT equipment. In the framework of the ONSITE European project, which deals with a hybrid (fuel cell and batteries) RBS (Radio Base Stations) supply system, a modeling activity is carried out to optimize the system operations. The developed algorithms separately implement a Solid Oxide Fuel Cell system and a high temperature Sodium Nickel Chloride battery for design purpose and collect them in a unique model for devices interaction (i.e. power production, storage, and control). Moreover, a Computational Fluid Dynamics battery model is developed to analyse the heat transfer while the SOFC stack generates excessive heat during operation and outlet hot gases can be effectively used. Since the SNC batteries need heat during charging process (to maintain their operating temperature) and, conversely, the reactions are exothermic in discharge mode, the described approach aims at combining SNC batteries with micro-CHP unit to optimize the energy flows. The implementation requires several alternative designs and variant analysis to secure proper operation of battery and power generation unit. The model developed and shown in this paper is a dedicated tool for the simulation of the hybrid system proposed and for the optimal designing of each main sub component. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.