ENERGIZE YOUR DC SYSTEM WITH POWER TO SPARE

Is choosing the right battery a test of your brainpower?

The average life of a car battery is 48 months. The average life of a marine cranking battery in recreational marine use is only 22 months. Marine batteries can last much longer if you make a few wise decisions about their selection, installation and
maintenance.

Story and Photos by Larry Blais

Replacing a battery in a car is a simple matter. The car’s manufacturer has determined the appropriate type, shape and capacity, and published these specifications. So all you have to do is decide what quality of battery you are willing to pay for. Recreational boats, on the other hand, are rarely equipped with batteries adequate to the power hungry  “gotta have” extra equipment that most of us think we need to enjoy boating. So, we approach the task of having to buy new batteries with some disdain, sometimes because the old ones either didn’t last as long as we thought they should or as long as we were told they would.

Capacity And Usage
If you need a battery for a small runabout with an outboard motor, deciding on a battery will be a relatively simple task but if you have a yacht with multiple engines, several radios, radar, refrigerator, inverter, etc., then the decision becomes more complicated. Let’s start with the simplest application and work our way up to the more complex.

 Any small boat that just needs a battery to start the engine and run some navigation lights from time to time can probably get by with just one Group 24 or 27 battery. Check with the engine manufacturer for its recommended minimum cold cranking ampere (CCA) rating required to start your engine and buy a quality marine battery with enough CCA capacity.

ABYC standard E-10 defines cranking performance (also referred to as marine cranking amps at 32°F/0°C or MCA at 32°F/0°C ) as “the discharge load, in amperes, that a new, fully charged battery at 32°F (O°C), can continuously deliver for 30 seconds and maintain a terminal voltage equal to or higher than 1.20 volts per cell.” The standard further states that, “Cranking batteries shall have at least the cold cranking performance rating (CCA at O°F/-17°C) or marine cranking performance rating (MCA at 32°F/0°C ) amperage required by the engine manufacturer.” For added peace of mind, consider adding a second battery of the same type and size. In any case, one battery or two, install a marine battery selector or On/Off switch. Although ABYC (E-9 and E-11) does not require these switches unless the battery output rating is at least 800 CCA, it’s still a good safety practice.

Adding an electric trolling motor? You’ll probably need a separate deep-cycle battery dedicated to its service. After a day of trolling, this battery can usually be at least partially recharged by your engine’s alternator if a battery isolation diode or selector switch is installed. If your boat has more than one engine, each engine should have it’s own cranking battery with a CCA rating appropriate for the engine’s need. Here again, adding a second battery or an emergency cross-over switch or a selector switch that would connect a cranking battery from the other engine would be prudent.

 If you operate lights, radios or other DC equipment without the main engine running (such as when at anchor or while under sail) or depend on a DC-powered bilge pump, then you may need a separate “house” electrical system energy source. This system is independent from the engine electrical system and has its own battery(s). House batteries should be true deep-cycle batteries that can tolerate deep discharge cycles between charging cycles. These batteries are rated in ampere hours (Ah). Because of the internal construction of these batteries, they rarely have the high ampere capacity to crank an engine and they can be damaged trying to do so. Likewise, cranking batteries, because of their internal construction, will not tolerate sustained discharging like deep-cycle batteries can.

 DC-to-AC inverters put very heavy demands on their host boat’s batteries. For a 12-volt inverter to supply 10 amps at 120 volts, it must draw over 100 amps from the batteries. To supply 20 amps, it would draw over 200 amps and so on. Having a dedicated inverter battery bank might be very wise.

A good quality 235 Ah golf cart battery can produce a continuous 75 amps for about 2 hours, 40 amps for about 4 hours, 20 amps for about 10 hours and 10 amps for about 25 hours. Since these batteries are only 6 volt each, two batteries must be connected in series to produce 12 volts and another set of these batteries connected in series may have to be connected in parallel to the first set to safely produce enough amps for sustained use of the inverter.

 Battery manufacturers are constantly looking for ways to satisfy the consumer’s needs. It would seem that a combination cranking/deep-cycle battery would be great idea. With the exception of a few very high-end batteries, most dual or combination starting/deep-cycle batteries are simply a poor compromise between a cranking battery and a deep-cycle battery and have not proven to be very good at either task. Be aware that some battery manufacturers have simply added handles and stud-type terminals to their standard cranking batteries and have sold them as marine deep-cycle batteries. Needless to say, they don’t last long.

Pick One, Just One

The top plate is from a heavy-duty deep-cycle battery used by railroads. The middle plate is from a popular deep-cycle battery used to power electric golf carts. The bottom plate is from a high-quality marine cranking battery. The plates in a typical car battery are more than 30% thinner than the plates in a high-quality marine cranking battery. The thinner more porous plates are more easily damaged. [Ed: One of the many reasons marine batteries are more expensive than automotive.]

Today, there are three distinct types of batteries available. They are flooded acid (a.k.a., wet cell), gelled acid (a.k.a., gel cell) and absorbed glass mat (AGM). Each type can be designed and constructed for either engine cranking or deep-cycle applications.
Flooded acid batteries are by far the most popular and generally seen as the most cost effective. Commercial vessels use them almost exclusively. Flooded low-maintenance batteries have filler caps and a lead-antimony/calcium dual alloy or hybrid plate formulation that helps reduce gassing. Flooded maintenance-free batteries are sealed and have a lead-calcium/calcium plate formulation that helps the hydrogen and oxygen gasses recombine back into water rather than needing to be vented.

The gelled acid batteries lost popularity very quickly partly because they require special low, slow recharging rates. Many gel cell batteries have been destroyed by being charged at the normal rate for a flooded battery. Sealed valve regulated lead-acid (VRLA) gel cell batteries are usually spiral wound and use a thickening agent like fumed silica gel to immobilize the electrolyte. The pressurized cells help hydrogen and oxygen gasses recombine back into water. They can withstand a deep discharge but not temperatures over 100°F (37.8° C) due to “thermal runaway.” They work best at an ambient temperature of 72° F (22.2° C). They generally produce less cold cranking amps than other batteries. Gel cells require longer recharging times at lower charging voltages. Of all the sealed batteries, the gelled acid battery is the least tolerant of the heat found inside most engine rooms.

The AGM battery has not faired much better, often due to improper installation. Sealed VRLA AGM batteries have a very fine fiber boron-silicate glass mat between their plates that absorbs and holds the liquid sulfuric acid. The pressurized electrolyte starved cells help hydrogen and oxygen gasses recombine back into water rather than needing to be vented.

Ventilate And Contain
Batteries must be protected against saltwater as this, mixed with electrolyte, produces deadly chlorine gas. Batteries also need to be protected against extreme temperatures. When underway, the temperature in boat engine compartments can exceed 120°F (48.8°C). A flooded battery loses half of its service life for every increase of 15°F (9.4° C) over 80° F (26.7° C). A hot engine compartment is not a good place for any battery.

All batteries need ventilation, even sealed ones, as they have pressure relief valves that will open if the battery is worked hard enough. Batteries, especially batteries connected to an inverter, can produce explosive hydrogen gas that should be vented to the outside of the vessel. Some modern yachts are built with power ventilation ducted right into the battery boxes, blowing the fumes overboard.

A battery On/Off or selector switch should be installed in the positive battery cable. It should be placed where it can be turned off without opening the engine compartment, just in case the compartment is aflame and opening the compartment would fuel a fire with an influx of oxygen. Select a switch with enough capacity to carry the current required without overheating the contacts. Overheated battery switch contacts often result in high resistance that keeps the battery from receiving a full charge and high resistance connections that overheat are a source of fire.

Tips For Longer Battery Life

Screw-down covers that hold these batteries securely in place, even in rough seas. They also cover the terminals so nothing metallic can short-circuit them.

Smart chargers and battery isolation diodes allow the alternators to charge multiple batteries.

This boat needs to be protected against acid spilling from the battery. A drip tray might help but a battery box is better. Note how these boxes attach to the boat by external screws. Never drill holes through the bottom of the boxes to fasten them down as this gives any leaking acid a path to leak from the container.

Normally all batteries “age” as the active positive plate material sheds due to the normal expansion and contraction that occurs during the discharge and recharge cycles. Eventually, this sediment builds up in the bottom of the case and can even short out the plates of a cell. The “aging” process is accelerated when the battery endures heat, vibration, overcharging, positive grid growth, positive grid metal corrosion, negative grid shrinkage, freezing, buckling of plates, loss of water or sulfation. Sulfation occurs when a battery drops below a full charge for long periods and hard lead sulfate crystals fill the pores in the plates.

Always wear protective glasses to protect your eyes in the unlikely event of an explosion when working with lead-acid batteries. [Ed: Read “The Day the Battery Box Exploded” on page 7 for a first-hand account of a battery explosion.] Battery plates need to be covered at all times to prevent an internal battery explosion or sulfation. Avoid overfilling, especially in hot weather, because the heat causes the electrolyte to expand and overflow. In an emergency, use rainwater rather than reverse osmosis or tap water because rainwater doesn’t contain calcium or magnesium. Using tap water to refill batteries can produce calcium sulfate crystals that fill the pores and coat the plates. Don’t add battery acid except to replace electrolyte spills.

Use an hydrometer to measure the specific gravity (SG) of the electrolyte in flooded acid batteries. This reading tells you the battery’s degree of charge. SG readings should not differ more that .030 between the lowest and highest reading. Use the following table to determine the battery’s degree of charge.

100%              1.265
75%    1.225
50%    1.190
25%    1.155
Discharged    1.120

(left) Note the black powder on the front of this engine. It formerly was part of the alternator belt. The belt pulley sheaves have rust pitted so badly that they are eating up the belt to the point that the belt is so loose that it's slipping. Sometimes sandpaper can smooth the pulleys. Sometimes the pulleys have to be replaced. If not attended to soon, the belt will fail. (right) This belt pulley is in better shape but is too loose and needs to be tightened until it deflects only about 5/16" to 3/8" (7mm to 9mm) when pushed with one finger.

Always charge with a “smart” or ”float” charger. An inexpensive, unregulated trickle charger can destroy a battery by overcharging it. Battery isolation diodes (also known as split charging diodes) allow the alternators to charge multiple batteries. These diodes have an inherent voltage drop of .6 volt to 1 volt that prevents them from fully charging the batteries unless the alternator output voltage is increased to compensate. If your alternator regulator doesn’t have an external adjustment, you may still be able to increase its output by installing a diode with the same voltage drop in the regulator sensing wire between the alternator and the regulator. This way the alternator “sees” the reduced voltage and increases the alternator output accordingly.

Clean and tighten any loose hold-down clamps, battery terminals and connectors. High resistance in a cable connector can keep the battery from receiving a full charge. Remove any corrosion with a brass wire battery brush by brushing the corrosion away from you. Take care to avoid poking yourself with the brush as a wound from the brush could lead to a serious infection. Neutralize heavy corrosion with a mixture of 1lb (.45kg) of baking soda (bicarbonate of soda) to 1gal (3.78L) of warm water. Be sure to keep this mixture from entering the battery cell where it can neutralize the acid. Treat the terminals with corrosion-inhibiting formula. Clean the battery top to eliminate conductive paths created by dried or wet electrolyte and to prevent corrosion.

Check alternator belt pulleys for corrosion and the belt for proper tension. A slipping belt prevents the alternator from properly charging the battery. Without being fully charged the battery will sulfate and lose capacity.

Most of the defective batteries returned to the manufacturers during the free replacement warranty period are still serviceable. This strongly suggests that an undiscovered problem with the electrical system was what prompt-ed the replacement of the original battery in the first place. Had this problem been discovered and corrected, the battery may not have even needed replacement.

If the electrolyte levels in non-sealed wet batteries (with filler caps) are above the plates but low, allow the battery to cool to room temperature and add only distilled, deionized or demin-eralized water to the level indicated by the battery manufacturer or to within 1/4" to 3/8" (6mm to 9mm) below the tops of the filler tubes, vent wells or splash barrels.

Caption: To use a hydrometer, simply hold the hydrometer vertically and squeeze the rubber bulb to force the air out. Now put the rubber tip into the electrolyte through the battery filler hole and release the bulb. The electrolyte is sucked up into the hydrometer allowing the float to ride freely. Read the SG at the point the surface of the electrolyte crosses the float markings. The SG reading should be between 1.100 and 1.300. Squirt the electrolyte back into the cell from which it was taken and record the reading. Repeat the process for each individual cell. Rinse the hydrometer with water when you’ve finished.