Marine Batteries, Battery Cable, and Battery Switches overview

What is a Marine Battery?

Marine batteries are essentially an electrical storage device that uses an electrolytic chemical reaction to store energy. Marine batteries use a combination of lead plates or grids and a sulfuric acid electrolyte that converts electrical energy into potential chemical energy and back again. Electrical systems that generate voltages less than 50 Volts are considered low-voltage. Typical low-voltage marine systems would feature 12 volts, 24 volts, 36 volts, etc. High performance marine batteries feature true marine grade design, construction and materials.

Marine storage batteries available for watercraft are one of several types: Flooded Lead Acid Battery (conventional wet cell); Gel Battery (Gelled Electrolyte); AGM Battery (Absorbed Glass Mat).

Selecting the an appropriate marine battery is not difficult once the various design types, advantages & disadvantages of each and the cost considerations are understood.

Flooded Lead Acid Battery (AKA Wet Cell)

The flooded lead acid type remains the most commonly available marine battery. The wet cell type is constructed in the widest variety of sizes and are built for many applications. Batteries of the flooded acid type are not sealed and will require the addition of electrolyte as the battery is charged. Due to the nature of the electrolyte (sulfuric acid) it is important that the battery be mounted securely and ideally be contained in a liquid tight, vented battery box. Remember, sulfuric acid + saltwater = chlorine gas!

Wet cell marine batteries are built in three basic configurations:

• STARTING BATTERIES: These batteries are designed for engine starting applications. They are not recommended for use in deep cycle (house) applications. Starter batteries feature thin lead plates which optimizes their ability to discharge a lot of energy very rapidly for short periods of time. Starting batteries do not tolerate deep discharges and are easily damaged if repeatedly discharged.
• DEEP CYCLE BATTERIES: Also known as "house" batteries, deep cycle types have heavier lead plates that allow them to be repeatedly discharged and recharged. Deep cycle batteries work well in trolling motor applications.
• DUAL-PURPOSE BATTERIES: As the name "dual-purpose" suggests, these batteries offer the capabilities of both an engine starting battery and a deep cycle battery. Naturally, this design is a compromise of two different construction types. Many sailing and power boats will have one engine starting battery and a deep cycle "house" battery. The engine starting battery has only one function and that job is an important one. Therefore, the starting battery should not be used as a power source for any other application. The house battery will typically power accessories and lighting systems: interior lighting, navigation lighting, radios, radar, electronics, etc.

Flooded Electrolyte Advantages:

• Lowest initial cost
• Higher cranking amps
• Water can be added (if accessible)
• Excellent for starting applications
• Tolerant of improper recharging voltage
• Some designs are appropriate for deep cycle applications
• Replacement batteries are available
• Good under extremely cold conditions when fully charged

Flooded Electrolyte Disadvantages:

• Spillable
• Must be installed upright only
• Shorter shelf life
• Do not install near sensitive electronic equipment
• Watering may be necessary (if accessible)

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Gel Lead Acid Battery (Gelled Electrolyte)

The gel cell lead acid marine battery uses a thickening material that immobilizes the electrolyte. Gel cell batteries are sealed and cannot have the electrolyte refilled. Gel batteries will not leak if inverted and can be mounted in a wide variety of locations that would be unsuitable for wet cell types. Gel cells will operate even if submerged under water.

Gel marine batteries are built in three basic configurations:

• STARTING BATTERIES: These batteries are designed for engine starting applications. They are not recommended for use in deep cycle (house) applications. Starter batteries feature thin lead plates which optimizes their ability to discharge a lot of energy very rapidly for short periods of time. Starting batteries do not tolerate deep discharges and are easily damaged if repeatedly discharged.
• DEEP CYCLE BATTERIES: Also known as "house" batteries, deep cycle types have heavier lead plates that allow them to be repeatedly discharged and recharged. Deep cycle batteries work well in trolling motor applications.
• DUAL-PURPOSE BATTERIES: As the name "dual-purpose" suggests, these batteries offer the capabilities of both an engine starting battery and a deep cycle battery. Naturally, this design is a compromise of two different construction types. Many sailing and power boats will have one engine starting battery and a deep cycle "house" battery. The engine starting battery has only one function and that job is an important one. Therefore, the starting battery should not be used as a power source for any other application. The house battery will typically power accessories and lighting systems: interior lighting, navigation lighting, radios, radar, electronics, etc.

Gel and AGM batteries are both also known as VRLA (Valve-Regulated Lead-Acid). Oxygen produced on the positive plates of all lead-acid batteries is absorbed by the negative plates. This reaction suppresses the production of hydrogen at the negative plates. Water instead is produced and retained within the sealed battery.

Gelled Electrolyte Advantages:

• Maintenance-free
• Spill proof & leakproof
• No corrosion
• Superior deep cycle life
• Installs upright or on its side (side install may reduce capacity by 10%)
• Very low to no gassing (unless overcharged)
• Compatible with sensitive electronic equipment
• Superior shelf life
• Superior rechargeability (from 0% to 90% in 3-1/2 hours)
• No recharge current limitation @ 13.8 volts
• Rugged and vibration-resistant
• Very safe at sea with no chlorine gas in bilge (due to sulfuric acid and seawater mixing)
• Versatile: Starting, Deep Cycle
• Operates in wet environment
• Will not freeze to -20 degrees F/-30 degrees C (if fully charged)
• Lowest cost-per-month (cost/months of life)
• Lowest cost-per-cycle (cost/life cycles)

Gelled Electrolyte Disadvantages:

• Higher initial cost
• Heavier weight
• Water cannot be replaced if continually overcharged
• Automatic temperature-sensing, voltage-regulated chargers must be used
• Charge voltage must be limited to extend battery life (13.8 to 14.1 volts maximum at 68 degrees F)

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AGM Lead Acid Battery (Absorbed Glass Mat)

The AGM lead acid marine battery uses a fiberglass-like material that controls the electrolyte. Like Gel cells, AGM batteries are sealed and cannot have the electrolyte refilled. AGM batteries will not leak if inverted and can be mounted in a wide variety of locations that would be unsuitable for wet cell types. AGM batteries will operate even if submerged under water. AGM battery construction results in them being highly resistant to vibrational stresses. AGM batteries are excellent in low temperature, high current applications like cold weather engine starting.

AGM marine batteries are built in three basic configurations:

• STARTING BATTERIES: These batteries are designed for engine starting applications. They are not recommended for use in deep cycle (house) applications. Starter batteries feature thin lead plates which optimizes their ability to discharge a lot of energy very rapidly for short periods of time. Starting batteries do not tolerate deep discharges and are easily damaged if repeatedly discharged.
• DEEP CYCLE BATTERIES: Also known as "house" batteries, deep cycle types have heavier lead plates that allow them to be repeatedly discharged and recharged. Deep cycle batteries work well in trolling motor applications.
• DUAL-PURPOSE BATTERIES: As the name "dual-purpose" suggests, these batteries offer the capabilities of both an engine starting battery and a deep cycle battery. Naturally, this design is a compromise of two different construction types.

Many sailing and power boats will have one engine starting battery and a deep cycle "house" battery. The engine starting battery has only one function and that job is an important one. Therefore, the starting battery should not be used as a power source for any other application. The house battery will typically power accessories and lighting systems: interior lighting, navigation lighting, radios, radar, electronics, etc.

Gel and AGM batteries are both also known as VRLA (Valve-Regulated Lead-Acid). Oxygen produced on the positive plates of all lead-acid batteries is absorbed by the negative plates. This reaction suppresses the production of hydrogen at the negative plates. Water instead is produced and retained within the sealed battery.

Absorbed Electrolyte Advantages:

• Maintenance-free
• Spill proof & leakproof
• No corrosion
• Installs upright or on its side
• Lower cost than gel cell batteries
• Very low to no gassing (unless overcharged)
• Compatible with sensitive electronic equipment
• Superior shelf life
• Superior rechargeability (from 0% to 90% in 3-1/2 hours)
• Rugged and vibration-resistant
• Very safe at sea with no chlorine gas in bilge (due to sulfuric acid and seawater mixing)
• Excellent for Starting applications
• Superior for short duration/high rate discharges
• Operates in wet environment
• Will not freeze to -20 degrees F/-30 degrees C (if fully charged)
• Lowest cost-per-month (cost/months of life)
• Lowest cost-per-cycle (cost/life cycles)

Absorbed Electrolyte Disadvantages:

• Shorter life cycle than gel in deep cycle applications
• Water cannot be replaced if continually overcharged
• Automatic temperature-sensing, voltage-regulated chargers must be used
• Charge voltage must be limited to extend battery life (14.4 to 14.6 volts maximum at 68 degrees F)

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Marine Battery Cable and Battery Terminals

Unlike ordinary automotive wire, marine grade battery cable is manufactured from tinned copper stranding for maximum protection against corrosion and electrolysis. Ultra flexible (Type 3) stranding is important because it resists mechanical fatigue due to movement, vibration and flexing. Marine grade wire and cable is constructed to American Wire Gauge standards, AWG wire is up to twelve percent larger than the equivalent SAE (Society of Automotive Engineers) wire sizes. AWG wire provides a greater current capacity when compared to SAE gauge wire.

When electrical systems are designed, the wire size is calculated for the specific requirements of the electrical components being used. When electrical components are added or upgraded, the wire size has to be upgraded also. For example, replacing a low torque starter with a high torque starter will normally require the battery cables and possibly the battery to be upgraded. When in doubt, always use a larger wire.

The size of a wire (gauge) is expressed in terms of a standard American Wire Gauge (AWG) measurement. The higher the AWG number, the smaller the wire. For example, a 14 gauge wire is smaller than a 10 gauge wire. The smaller the wire, the greater its resistance to the flow of electrons and the greater the heat generated when the wire is conducting electricity. This heat can destroy insulation and even ignite a fire. The larger the amperage of a circuit, the larger the wire that is needed.

Marine battery cable is available in a wide variety gauges to suit virtually any application. Battery cable is available in pre-made sizes with terminals attached or in bulk rolls where custom cable lengths are required.

Marine battery cables feature a heavy duty vinyl insulation that stays flexible in extreme cold while resisting seawater, battery acid, oil, gasoline, diesel fuel and ultra-violet radiation. Most cable is manufactured with vinyl insulation color coded for several applications. RED cable is typically used as DC Positive conductor; BLACK or YELLOW is used for DC Negative conductors. YELLOW is normally used in DC installations where AC power systems may exist where BLACK indicates the "HOT" circuit.

Marine AWG battery lugs or terminals are manufactured from heavy duty annealed tinned copper, that provides for maximum current flow. 100% tin plated copper lugs are designed to resist corrosion from salt and moisture. A seamless barrel design allows for maximum strength when crimped. A properly crimped terminal with adhesive lined shrink tubing seals out moisture so that battery cables remain dry and corrosion free. In order to ensure the proper assembly of lugs and cables it is recommended that only high quality stripping and crimping tools be utilized.

Corroded or worn battery cable lugs can be the source of all sorts of problems. When an engine starter is engaged a poor connection can result in a heavy electrical arc which can possibly destroy the battery post. If the battery is gassing, the arc could cause the battery to explode. Never use the temporary type battery ends for permanent connections. Temporary terminals are only good for emergency use and will corrode and fail quickly. Always replace a worn terminal with a crimped and sealed battery cable end or replace the entire battery cable assembly.

Battery cable terminal boots provide extra protection for the terminal and cable connections. Color coded cable boots add a professional, finished look to the cable runs while insulating the positive and negative battery poles, helping to prevent accidental short circuits.

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Marine Battery Switches

All boats that have an electrical system should have at least one master battery-disconnect switch. The correct location of this switch is very close to the battery and it must be easily accessible. The master disconnect switch is necessary so that the entire electrical system can be turned off at the source. It is usually a good idea to turn off the power when a boat is left unattended for a period of time. A master shut-off switch is absolutely essential during an emergency- short circuit, electrical fire, etc.

Boats with multiple batteries (starting, house) should have battery selector type switches. Battery selector switches connect and control multiple batteries while isolating them from each other. Typically, only one battery will receive a charge when the engine is running. Multiple batteries can be charged simultaneously if the selector is set to the "BOTH" position. Once charged, it is not advisable to leave the switch in the "BOTH" position due to the possibility of discharging two batteries at once.

Many high quality battery switches incorporate alternator field disconnect (AFD) feature. The field disconnect capability is important in that it can prevent expensive damage to the alternator should the switch be accidentally set to "OFF" while charging a battery.

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Marine Battery Boxes and Trays

Rugged marine battery boxes simplify installations and typically feature seamless, heavy wall construction that provides superior chemical resistance. A well made battery box will eliminate any concerns regarding electrolyte spills or contact with grease, oil or seawater. Quality battery boxes are made of molded polyethylene designed to maintain tough impact properties down to -40F. The box case should feature full flow ventilation to ensure adequate cooling to improve the service life of the battery. Battery trays are also designed to improve battery installations and to securely hold them in place.

Never install any type of battery in a completely sealed container. Oxygen and hydrogen will escape from any battery when it is in an overcharge condition. These explosive gases must be vented to the atmosphere and must never be trapped in a sealed battery box or container.

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Marine Electrical Resources

Boatowner's Mechanical and Electrical Manual 3rd Edition<, by Nigel Calder, is an excellent resource and an essential troubleshooting guide for any boater, from the extreme novice to seasoned veteran. If it is on a boat and has screws, wires, or moving parts, it is covered in the Boatowner's Mechanical and Electrical Manual. Nigel Calder provides comprehensive advice on: battery technologies, 12 and 24 volt DC systems, corrosion, bonding & lightning protection, generators, inverters, battery chargers, electric motors, electric lights, marine electronics, antennas, RFI, diesel engines, transmissions, shaft brakes, and propellers.

The Electrics Companion, by Pat Manley, will help you figure out how much energy you are consuming and how much each item uses per day. Most of the equipment we 'switch on' consumes electricity, even the panel lights and voltmeter all add up. Author Pat Manley's guide will help you understand your battery capacity and charging requirements.

Simple Boat Electrics, by John Myatt, contains all the information needed to troubleshoot 12-volt electrical systems. It explains how to locate a fault, correct the problem when you can, or adopt a "get-you-home" solution if you can't. Provides some basic theory so you can understand what you're doing with a special emphasis of seamanlike practice of anticipating and preventing trouble.

The Arco Electrical Technical Manual, is packed with information to help you become more proficient in servicing sophisticated marine electrical systems. The Arco Electrical Technical Manual explains the fundamentals of troubleshooting electrical systems. Written in easy to read style with lots of illustrations and examples. Written by mechanics for mechanics.

The 12 Volts Made Easy - DVD, is a nuts and bolts 12 volt electrical systems primer that is presented in a clear and easy manner. Subjects covered include: basic electrical theory, circuits, battery maintenance, basic wiring diagrams, controls, transducers, recharging, marine components, lights, motors, troubleshooting, basic repairs, installations, and more. Running Time: 60 minutes.

The 12 Volt Sailor - DVD, will help you to learn how to design and build an efficient electrical system for any vessel. This program illustrates how to integrate the radar, watermakers, windlasses, single side band radios, auto pilots, and GPS devices into any D.C. System. Running Time: 45 minutes.

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