Boat Batteries

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Boat Batteries

An electric battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. Electrolytes allow ions to move between the electrodes and terminals, which allows current to flow out of the battery to perform work.

Most boats are equipped with rechargeable batteries of some kind which can be discharged and recharged multiple times. Charging a battery typically involves running a current in reverse through a the charge, i.e. applying a voltage across the battery to create a current stronger than the battery current, so that the current flows from - to + instead of from + to - inside the battery.

Battery Types

Trojan T105 deep cycle battery - click for larger view

Wet Cell (flooded) Lead Acid Batteries

The lead–acid battery was invented in 1859 by French physicist Gaston Planté and is the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with their low cost, makes them ideal to supply the high current required by starter motors.

The main advantage that they have is that they are inexpensive compared to newer technologies. Lead-acid batteries are widely used even when surge current is not important and other designs could provide higher energy densities. Modified versions of the standard cell may be used to improve storage times and reduce maintenance requirements. Gel-cells and absorbed glass-mat batteries are common in these roles, collectively known as VRLA (valve-regulated lead-acid) batteries.

Lead–acid battery sales account for 40–45% of the value from batteries sold worldwide.

Deep Cycle vs Starting Batteries

A deep-cycle battery is a lead-acid battery designed to be regularly deeply discharged using most of its capacity. In contrast, starter batteries are designed to deliver short, high-current bursts for cranking the engine, thus frequently discharging only a small part of their capacity. While a deep-cycle battery can be used as a starting battery, the lower "cranking amps" imply that an oversized battery may be required.

A deep-cycle battery is designed to discharge between 45% and 75% of its capacity, depending on the manufacturer and the construction of the battery. Although these batteries can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 45% discharge.

Deep cycle batteries are manufactured with thicker plates that hold a higher charge for longer. The downside of the thicker plates is that they do not easily release a large current. Starter batteries, on the other hand, are manufactured with thinner plates that are capable of delivering a higher current, but in turn do not hold as high a charge as deep cycle batteries and are more easily damaged by deep discharge.

Absorbed Glass Mat Batteries

AGM batteries differ from flooded lead acid batteries in that the electrolyte is held in the glass mats, as opposed to freely flooding the plates. Very thin glass fibres are woven into a mat to increase surface area enough to hold sufficient electrolyte on the cells for their lifetime. The fibres that compose the fine glass mat do not absorb nor are they affected by the acidic electrolyte.

AGM batteries can be used for either deep cycle or starting purposes.

The main disadvantage of AGM batteries over flooded lead acid batteries is the additional cost.

Gel Cell Batteries

A modern gel battery (also known as a "gel cell") is a VRLA battery with a gelified electrolyte; the sulphuric acid is mixed with fumed silica, which makes the resulting mass gel-like and immobile. Unlike a flooded wet-cell lead-acid battery, these batteries do not need to be kept upright. Gel batteries reduce the electrolyte evaporation, spillage (and subsequent corrosion problems) common to the wet-cell battery, and boast greater resistance to shock, and vibration, making them attractive in marine environments. Chemically they are almost the same as wet (non-sealed) batteries except that the antimony in the lead plates is replaced by calcium, and gas recombination can take place.

Gel cell batteries are typically only used in deep cycle applications.

Lithium Batteries

Lithium Battery -- click for larger view

Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of rechargeable batteries for portable electronics, with a high energy density, no memory effect, and only a slow loss of charge when not in use. Beyond consumer electronics, Lithium batteries are also growing in popularity for marine applications.

Lithium batteries offer much better energy density than lead acid batteries, as well as significant weight advantages, however at a much higher cost.

Newer boats fitted with electric motors in place of the traditional diesel powered inboard are increasingly moving to Lithium battery technologies.

Catamaran owners are often attracted to Lithium batteries due to their much lower weight for the same charge.

There are an increasing number of types of Lithium battery, for example:

Installation

Details?

Charging

See Power Generation

Maintenance

See Battery Care

Forum Discussions

List links to discussion threads on partnering forums. (see link for requirements)

References

Publications, etc.

External Links

Also See


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Names: Delatbabel


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