by Lea Miller

Created on: October 13, 2010

All sorts of vehicles require batteries to help them function as they were designed to do. While both automobiles and boats rely on lead-acid type batteries, the output of those batteries is designed for different purposes. Because of these different designs, it's not possible to use an automotive battery in a boat or a marine battery in a car.

A lead-acid battery works by immersing plates of lead and lead dioxide in a dilute sulfuric acid solution. The chemical reaction between the plates and the sulfuric acid produces lead sulfate and free electrons, which create an electric current. A single cell of a lead-acid battery produces about two volts, so combining six cells yields a battery with a capacity just over 12 volts.

Sending an electrical current back into the battery re-forms the lead and lead dioxide layers on the plates, thus renewing the battery and making it possible to reuse it many times. This recharging process happens when the engine is operating and the alternator is running. This is also why a car battery can be recharged by connecting the spent battery in one car to a fully charged battery in another car while the engine is running.

An automotive battery is designed to produce a lot of current quickly, so there is enough power available to crank the engine during ignition. During the normal operation of the vehicle, the alternator is producing the bulk of the power required, so the battery is intended mainly to produce the quick power surge needed for starting. To accomplish this, the battery contains many thin plates with a large surface area. The lead plates react quickly to produce power but not much is left in reserve after the initial boost. The battery is not designed to be discharged beyond 20% of its capacity for an extended period.

The chemical reaction in the battery is rated for the number of amps produced at 32 degrees F. (0 degrees C.), usually referred to as cold cranking amps (CCA). The battery is also rated for reserve capacity (RC), which measures its ability to sustain a certain amperage level while maintaining more than 10.5 volts.

A marine battery is a compromise between an automotive type battery and the type known as a deep cycle battery. A deep cycle battery is designed to produce a steady current over a longer period of time and to discharge substantially all its power repetitively, and is not designed to produce a quick power surge. Deep cycle batteries have a higher reserve capacity than automotive batteries and a lower rating for cold cranking amps. The deep cycle battery is designed with a small number of thick lead plates.

A marine battery has somewhat thicker plates than an automotive battery, but less than a true deep cycle battery. It is capable of discharging near half its capacity before recharging. While boats also have alternators, if the marine battery is operating multiple electrical appliances such as GPS, navigation lights, trolling motor, etc. while the engine is not running, the alternator has no chance to recharge the battery. To recharge the batteries, it may be necessary to run the engine for a longer period or connect the marine batteries to a recharger at the dock.

Battery designs are specific to the usage. Follow manufacturer recommendations for maintenance and care, and good quality batteries for both cars and boats should give long reliable service.

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