Really, If I understand it correctly, you don't really waste you battery using the cigerrete lighter, while the car is on at least, because while to engine is running, it is charging the battery, and the main reasons there is a battery is for all the electronic things in the car, and most importantly starting the car. Unless you wanted to use it out of the car, or when it was off, then the battery would probably be better. Do you already have an electric cooler, if so then all you would have to do is put the panels on the top of the car or werever you plan on putting them, and then getting a converter, and a transformer(you can get them off ebay) to change whatever you got from the solar, to match with whatever the cooler needs.