Design

Starting batteries, also known as high-torque batteries, have high cranking amps, but lower reserve time ratings. Deep cycle or dual purpose batteries can also have high cranking power, but they have higher reserve capacity as well. This allows more discharge/recharge capability.

Deep Cycle batteries are helpful in situations where you have a lot of electronics, a trolling motor, etc. Automotive batteries are usually lighter construction and lower reserve time.

Heavier construction, e.g. thicker plates, makes marine batteries stronger. This allows them to better tolerate the conditions they are exposed to in marine use. There is a common misconception that automotive batteries, engine parts, etc. are interchangeable with marine parts. There are many differences in construction, especially when related to anything involving electrical, fuel, or the dampness inherent to boating. Safety is always an important factor, and stronger tolerance to the abuse of marine situations is also an issue.