quote:4.2. Type
Car batteries are especially designed for high initial cranking amps (usually 200 to 400 amps for five to 15 seconds) to start a car and for shallow (10% or less) discharges. They are not designed for deep cycle discharges. Deep cycle (and marine) batteries are designed for prolonged discharges at lower current and not for high current discharges. The plates in a car battery are more porous and thinner than in deep cycle batteries and use sponges or expanded metal grids instead of solid lead. A deep cycle battery will typically outlast two to ten car batteries when used in deep cycle applications. In warm weather, starting an engine will typically consume less that 5% of a car battery's capacity. In contrast, deep cycle (or marine) batteries are used for applications that will consume between 20 and 80% of the battery's capacity.
A dual or starting marine battery is a compromise between a car and a deep cycle battery that is specially designed for marine applications. A deep cycle or dual marine battery will work as a starting battery if it can produce enough current to start the engine, but not as well as a car battery. For saltwater applications, AGM or gel cell batteries are highly recommended to prevent chorine gas.
For RVs, a car battery is normally used to start the engine and a deep cycle battery is used to power the RV accessories. The batteries are connected to a diode isolator. When the RV's charging system is running, both batteries are automatically recharged. An excellent and easy to understand free booklet on multi-battery applications, Introduction to Batteries and Charging Systems, can be obtained by calling (800) 845-6269 or (503) 692-5360.
The two most common types of deep cycle batteries are flooded (also known as wet or liquid electrolyte) cell and valve regulated (VR). These types are divided into Marine and RV batteries. There are 50% depth-of-discharge limits and sponge lead plates batteries, and there are the more expensive Deep Cycle (traction and stationary) batteries with 80% depth-of-discharge limits, solid lead plates, and longer lives.