The difficulty in designing gears to be installed in electric vehicles is caused by the fact that the efficiency of gears is generally treated as a constant value in the entire operating range, while these show significant differences in different operating ranges; therefore, it is necessary to examine the energy and efficiency of the gear, and to create a mathematical model, which can be optimally fitted into the vehicle’s drivetrain in terms of energy. I have performed this modeling in previous years for a single-stage gear unit. However, this model encounters physical limitations, since a larger gear ratio modification cannot be performed in one stage; the number of stages must be increased as the gear ratio increases. As the number of stages increases, the structure of the mathematical model changes, as changes to the gear unit must be incorporated into the model. In this article, an extension of the mathematical model of the gear unit is presented.