The growing deployment of electric mobility calls for static and dynamic grid studies to investigate to which extent it affects the grid operation and how to validate the countermeasures. Detailed electric vehicle (EV) models, which allow analyzing electrical variables at the EV charger and battery levels, are inadequate for this purpose, as they can have an excessive complexity and are computationally burdensome for large-scale grid studies. To address this issue, we exploit a detailed EV model using an analytical approach, and develop an equivalent model of EVs with fast chargers that is easy to implement and computationally efficient, while retaining adequate accuracy. Simulation results of distribution and transmission systems, modified by adding fleets of EVs, are used to demonstrate the compatibility of the proposed model for static and dynamic grid studies, even when different cathode chemistries and charging strategies are adopted.