The way current is delivered to the application is a major difference between a deep cycle and car starting battery. The latter is designed to provide a large amount of current over a short period of time. The current must be enough to overcome the compression in the engine and turn it over fast enough to start. A deep cycle battery is designed to provide a continuous flow of lower amperage current over a long period of time.
Contrary to automotive battery design, which incorporates a large number of thin lead plates in order to provide the largest surface area and a burst of current quickly, a deep cycle battery is built with much thicker plates that hold a charge for a longer period of time. Also, a deep cycle battery's plates are made of solid lead, while a car battery is more of a sponge design, once again, for maximum surface area. A deep cycle battery would not work well in a car because it wouldn't have the necessary all-at-once charge to turn the engine over. However, these batteries are sometimes used in cars that have large power draws from accessories, such as powerful audio systems.
A starter type battery is found in automotive applications, primarily vehicles with internal combustion engines that require the aforementioned "burst" of current to start. A deep cycle battery has many uses, however: golf carts, fork lifts, traffic lights, trolling motors, race cars without an alternator charging system, snow plows and aftermarket audio systems are a few examples of where one might commonly be found. The idea to keep in mind is that any application demanding constant low power needs a deep cycle battery.
A properly maintained deep cycle battery used in the manner it was designed for has the capability of lasting years, perhaps as many as 25. The term "deep cycle," from which it gets the name, means that it should be used down to where there is only 10 to 20 percent charge left before being re-charged, which might be a period of several weeks or months depending upon use. At the bottom of each deep cycle, the battery should be recharged. A good deep cycle battery can last up to about 150 deep cycles, according to solar electricity retail specialty store, Northern Arizona Wind & Sun.