Installing a home facility in a car?

Good evening And I have an old Fiat Tempra 1.6. Unfortunately the sound quality is very modest and the bass is missing completely. And since I want to invest little money in the car, I thought because I have such a small plant (http://www.amazon.de/gp/product/B002VV9NZO) at home, that I connect it with such a voltage converter (http://www.ebay.de/…/31361282941?…) to my cigarette lighter. What do you think of this idea? Is it going to suck my 12V car battery empty? t or do I only expect a higher fuel consumption? I would of course only listen to music when the car is running. Plant consumes about 50Watt. Thanks in advance. Chris