You're using a deep cycle battery as the only battery in your car???
A deep cycle battery is for operating accessories over long periods of time. Then you put it on a charger. It's OK as a second battery in a system. Regular car batteries are built to start your car, after that the alternator kicks in and provides the power for all the electrical devices in your system when the car is running. When your car is running it recharges your battery so it starts up the next time. A deep cycle battery needs a long slow charge, that's way they are used for trolling motors.
Try a regular car battery. I'm guessing that's your problem.