In this paper, we introduce a discrete-time model for the complete power supply sub-system that closely approximates the behavior of its circuit-level (i.e., HSpice), continuous-time counThe model is abstract and e cient enough to enable event-driven simulation of digital systems described at a very high level of abstraction and that include, among their components, also the power supply. Therefore, it can be successfully used for the purpose of battery life-time estimation during design optimization, as shown by the results we have collected on a meaningful case study. Experiments prove also that the accuracy of our model is very close to that provided by the corresponding Spice-level model.