There has been an old rule that I don't believe will ever be changed. It says you lose some of the energy that is being used to power something. It's something that always happens. I can't remember how the law is stated; but something about you can't get the same amount of work from something as the amount of energy it takes to run it. It just can't be done; at least not with the knowledge that we have now.
According to the Law of Conservation of Energy, energy can neither be created nor destroyed; it can merely be converted from one form to another. Here's a fairly simple description of what's going on:
In this particular application, say that we want to drive a 1 kW generator to power the battery in our car. We can't simply create this power - we use the generator to convert energy from one form (mechanical) to another form (electrical.) Assuming that this generator were 100% efficient - and as this is only possible in theory, as in practice it would be far lower than this - if you put 1 kW into the generator in terms of mechanical energy, you'd get 1 kW of electricity out the other end. Essentially you'll have accomplished nothing but make the vehicle heavier than it needs to be.
However, 100% efficiency is an ideal that doesn't actually exist. Let's say that our ultra-high-efficiency generator is 60% efficient, which is about the state of the art these days. That means that your kW of mechanical energy just left as 0.6 kW as electrical energy - you actually lost energy instead of gaining it, and again, the car is heavier than it needs to be. Better to just get rid of that generator and save some weight and 0.4 kW, right?
One rather nice trick used on a lot of electrics and hybrids is what's called regenerative braking. When the brakes are applied, the drive motor(s) is/are coupled to the wheels in some fashion and the momentum of the vehicle is used to turn the motor. We all know that a motor will turn when electricity is supplied to it, but the reverse is true as well: if you turn a motor, it produces electricity. This is all an alternator is at the end of the day, a little motor that's being turned by the engine. By doing this, the momentum of the car is converted into electricity, which can then be used to recharge the battery. There is no free lunch here though...we're stealing energy from the car to give to the battery, and at a fairly poor efficiency level to boot. But it's better than nothing, as conventional braking converts that energy to heat (via friction between the brake pads and the brake discs) and effectively wastes it.
This is why wind turbines, additional motors, or other mechanically-driven add-ons will not allow you to recharge the battery in your car. Actually they will, but they'll consume more battery power than they'd provide. That's why you don't see them. The engineers are not out to screw anyone. They simply understand the problem better than most consumers do.
In a roundabout way, this also addresses why we can't simply reprogram the ECU's in the cars in order to make them get better fuel economy. Actually, we sort of can, but only by having the engine burn less fuel. Gasoline is merely energy stored in a chemical form, and one gallon of gasoline contains a fixed amount of energy. When we burn it efficiently (which internal combustion engines simply don't do, as a result of all that pumping and blowing and rotating and stuff), we can only get out that amount of energy - no more. That's all that there is.
The internal combustion engine, as currently used, is only about 40% efficient or so. I don't see that increasing very much. There are just too many power losses through the design...I mean, hell, just consider the radiator! We have to install a major subsystem on our engines specifically to steal energy from it! (All that heat that the radiator removes in order to keep your engine from seizing up is energy that came from your fuel, but is wasted as heat. The electricity that powers your accessories, the compressor that handles the refrigerant for your air conditioning...all of these things take energy from your engine, and that's before we get to frictional losses in the drivetrain and the engine itself. Like I said, these things are not and cannot be efficient.) If we want to increase that significantly, I think that it will take a completely new design and a lot less features on the cars...and even then, it might not be much better. The fact of the matter is that it's very, very difficult to convert energy from one form to another efficiently, and that's what we're doing when we burn gasoline to move an automobile.
