Robust design of microgrids is a complex optimization process requiring multiple simulations in order to integrate uncertainty variables associated with the system environment or design models. In this context, having sufficiently accurate models that are compatible with the optimization algorithms and associated computational costs represents a real challenge. In this paper, we illustrate this through the robust design of a simple microgrid with electrochemical storage. Based on battery models that couple energy efficiency and aging, we develop an approach for choosing the right level of precision to match the microgrid's optimization criteria or constraints.