In order to charge a car battery, a solar car battery charger transforms ultraviolet light—typically from the sun—into an electrical current. The majority of low-cost solar car battery charger products have very low power levels. As opposed to actual battery chargers, they are categorized as trickle chargers. These chargers can only provide up to one Amp to charge the battery in your automobile. More of a battery caretaker than an actual charge, this charging rate. They are not made for batteries that are fully dead; rather, they are made for cars that sit for longer periods of time. A completely dead battery will need at least an entire day to charge up enough to possibly start a car.
There are types that can deliver up to 10 Amps, and this is enough to quickly recharge a dead battery. These devices do, however, cost several hundred dollars.