[gone-ot]

Every 746 Watts of electrical power is 1 HP.

So, if you figure each headlamp draws 10 Amps on 'highbeam' that would be 294 Watts, or 0.39 HP, of continuous power.

Now, add in all the 'other' electrical components that are drawing their power from the BATTERY/ALTERNATOR system and you've probably got an electrical "load" of 2-5 HP.

Since the 'typical' car requires about 15 HP at 55 MPH for movement, that means the engine is being asked to "put-out" 33% more power just to accommodate that 2-5 HP electrical load...and HP eats fuel, just like you and I eat food for energy.