The radio is powered by electricity, which is energy. This energy has to come from somewhere, that somewhere is the battery
The battery is charged by the alternator, the alternator converts kinetic energy from the engine which is turning, into electrical energy which is then stored in the battery
The energy which is turning the engine is converted from chemical energy stored in the fuel, to kinetic energy, by the good old internal combustion engine we all know and love (or compression ignition in the case of diesel)
And even the electricity generated whilst you are decelerating, and so not actually burning any fuel, is simply energy that was converted from chemical (fuel) to kinetic (momentum) during acceleration and is now being recuperated !
So there ya go, even listening to the radio is not free
![Shake :shake:](./images/smilies/nol2.gif)