The starter motor circuit (1) comprises a combination (10) of a starter motor and of a device (LPF) for stepping up the battery voltage. The device for stepping up the battery voltage is intended to prevent a drop in battery voltage caused by a current spike that appears in a power circuit of the starter motor when power is applied thereto. The starter motor in the conventional way comprises an electric motor (DCM) and an electromagnetic contactor (EC). The device for stepping up the battery voltage is a filtering device of the inductive type which is mounted in series with the electric motor in the power circuit and comprises a casing made of magnetic material, a primary winding circuit intended to be inserted in series in the power circuit, and a secondary winding circuit mounted as a short circuit.