Car batteries are specially designed with thinner (.04 inch or 1.02 mm) and more porous plates for a greater surface area to produce the high amps required to start an engine. They are engineered for up to 5,000 shallow (to 3%) discharges, which works out to over four engine starts per day. Car batteries should NOT be discharged below 90% State-of-Charge. They use sponge lead and expanded metal grids rather than solid lead. Marine Starting batteries are a comprise between a car and deep cycle battery and are designed for starting and prolonged discharges at lower amperage that typically consumes between 20% and 50% of the battery's capacity. Motive and Stationary deep cycle batteries have much thicker (up to .25 inch or 6.35 mm) plates, more lead, and weight more than car batteries the same size. They are normally discharged between 20% and 80% at lower amperage. deep cycle batteries will typically outlast two to ten car batteries in a deep cycle application.