If it hasn't happened to you yet, it will: You wake up to a dead car battery. Should've made sure those headlights were really off, smart guy. The Sunsei SolarCharger 135 by ICP Solar can prevent this tragic turn of events by keeping your battery topped off with power from the sun.
Just lay the solar panel on the dashboard or if you prefer, attach it to the inside of the windshield using the enclosed suction cups. The panel is designed to work though glass, so by leaving it in the sun you'll always have a full charge. It should work even if your vehicle hasn't been started in a while. Used more as a maintenance product than a charger, the Sunsei provides "trickle down" power, keeping your battery charged and healthy while never overcharging it. It works with any 12-volt vehicle including boats.