The device has a controller (6) with an algorithm for electrical energy management a sensing arrangement (9) for detecting different driving states at least one controllable load (5) and a generator (1) with a generator output voltage regulator(2). At least one load is controlled so that the electrical load power increases and/or the generator power increases in driving states with high internal combustion engine efficiency. In low efficiency states at least one load is controlled so the load and/or generator power reduces.