Differences between a “car" battery and a "deep cycle" battery.

• People who have boats are familiar with deep cycle batteries. The sun or wind etc. produces power during the day and the batteries store some of the power for use at night.
• Both car batteries and deep cycle batteries are lead-acid batteries.
• A car's battery is designed to provide a very large amount of current for a short period of time. This is needed to turn the engine over during starting. Once the engine starts, the alternator provides all the power that the car needs, so a car battery may go through its entire life without ever being drained more than 20% of its total capacity. Used in this way a car battery can last a number of years.
• To achieve a large amount of current, a car battery uses thin plates in order to increase its surface area.
  A deep cycle battery is instead designed to provide a steady amount of current over a long period of time.
• A deep cycle battery can provide a surge when needed, but nothing like the surge a car battery can. A deep cycle battery is also designed to be deeply discharged over and over again (something that would ruin a car battery very quickly).
• To accomplish this, a deep cycle battery uses thicker plates.

Info courtesy Rolls batteries