R. Karl

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In General

Don’t let the “maintenance free” battery in your car lull you into complacency about the battery in your boat. Neglecting a marine battery is certain to shorten its life. Get the most from your boat’s batteries by following these guidelines:

• Keep idle batteries fully charged. Leaving a battery even partially discharged leads to sulfation and loss of capacity.
• Check the water level regularly. Top off as necessary to keep the level about 1/4” above the plates.
• Use only distilled water for topping off the battery; trace minerals and/or chlorine in tap water really do shorten battery life.

I recommend the Dual Pro 15 Amp/Bank Professional Series 2 Bank Charger for onboard charging.

Question from Frank about Chargers:

Hello!
I was reading your article and I have a question about battery chargers. When you say to get a charger that is rated about 15% of the battery’s amp-hour rating. Where do you find that on the specs of the battery. I have found as follows on the deep cycle SRM-29:

*CCA = 675 Cold Cranking Amps
*MCA = 845 Marine Cranking Amps
*RC (Min) = 210 minutes Reserve Capacity
Hours at Ampere Load:
@5 Amps = 21 Hours
@15 Amps = 6.4 Hours
@25 Amps = 3.4 Amps
I haven’t seen a batteries amp hour rating of 200 amp hours!
Thanks for any info. I am looking to buy a charger for my two batteries over the winter.
Frank

Answer:

Hi Frank –

Ampere-hour ratings are simply the number of hours that the battery will last under a particular load. Although many batteries are rated at 125 Ah, 250Ah batteries are out there – and not all that uncommon these days – especially with all the additional electronics that are on today’s boats! On your battery – as is the case on all – the numbers indicate the length of time you can expect to have the battery function properly under the stated load: for instance, 5 amps x 21 hours = 105 Ah. As the load increases, the length of time will decrease: 25 amps at 3.4 hours is only 85 Ah! My guess is that your battery is probably a 125 Ah model. (Although one would think that a battery rated at 125 Ah should run 10 amps for 12.5 hours, in reality it simply will not – lots of Chemistry and Physics there…)

So, if you have a 125 Ah battery, you would generally be looking for a charger that can deliver 15% of that, or approx. 20 amps. Then, as a rule of thumb, take the Amp-hour rating of the battery and divide it by the charger rating (amps). Then add about 10% for the extra time to totally top off the battery, This will give you the approximate total charge time. In your case, your battery should take about 7 hours to charge using a 20-amp charger… but there are many other factors to consider when charging your battery: How much charge is left? What is the condition/age of the battery? What kind of charger do you have? Etc., etc., and etc.

Just remember that a battery can, by self-discharging, lose about 4% – 5% of its charge per week. So, in one month’s time just sitting in a warm garage, a fully charged battery that started at 125 Ah may now have maybe 105 Ah available. Not charging it at all over a four-month period can have disastrous effects! A good charger is even more important than a good battery. And, as has always been the case… you get what you pay for. I recommend a multi-stage charger with auto shut-off. And check the voltage regularly. Never let a battery drop below 80% of its rated voltage. For a 12-volt battery (which, fully charged, should register about 12.7 volts), that’s about 10 volts.

Best,
RK

Question from Jane about Boat batteries for intermittent storage

Your article is great for long term battery storage. We are faced with summer storage (indoor) without electricity in Arizona, so the indoor temps probably reach 130+. The boat could sit for 2-4 weeks between uses. Pulling the batteries is a pain in this boat, so I would rather not have to do that with each trip. This is a jet boat and has a switch by the batteries that can be: Battery 1, Battery 2, or Off. If we switch it to off, is that the same as pulling the batteries. Someone suggested that we could disconnect the negative connection. You seem to understand batteries so what would you suggest or maybe you aren’t available for suggestions. Just thought I would try. Thanks for your time!

Jane

Answer:

Hi Jane –

You didn’t say what kind of batteries you have or for what they are specifically used. But, in general, there are basics to know for all batteries when it comes to caring for them. My assumption is that you are storing your boat at a location away from your AZ house – which is why you have no access to electricity for charging? Extremes in temperatures are bad for batteries… but heat is a much greater foe. And while it may not be quite as bad for a cranking battery – it gets recharged by the engine while it is running – not charging trolling motor (i.e., deep cycle) batteries immediately upon returning from a fishing trip will shorten their life drastically… for a number a of reasons.

One of those is called “internal battery discharge”. Parked in storage with temperatures like you described will quickly weaken your batteries, even if they are brand new and fully charged when the boat is parked. Opening up the battery box compartment may help some, but not much at those temps. Something called sulphation is always trying to occur. This is a process whereby sulfur molecules in the sulfuric acid electrolyte solution begin to coat the lead plates in your battery. It’s very much like plaque building up in your arteries.

The coating continues to thicken until the battery eventually fails. Sulphation occurs mostly in batteries whose electrolyte level is low, leaving the lead plates exposed. So, it obviously is important to make sure that electrolyte level in the batteries is topped off (use only distilled water) so that the plates are covered. But it can also occur – and more rapidly so – in deep-cycle batteries that are not fully charged as soon as possible after use. Every minute you delay contributes to sulfation. And if they only get recharged to, say, 80%… then that leaves a 20% opening for sulfation. This of course is exacerbated by the high temperatures in storage.

All that said – without electricity to keep the batteries charged between outings – the life of your batteries will definitely be shortened by a lack of proper care for them. As much of a pain as it might be to remove the batteries after each trip, leaving your batteries in the boat is definitely going to be detrimental for their survival. If your only option is to disconnect them, it would be better than to just switch them off, as there is always a tiny power drain when wires are connected. Then too, if you have no deep-cycle batteries, at least you will have less of a problem…

Bottom line: purchase the freshest batteries you can find with the greatest amount of RC (reserve capacity) available. And then look after them with the same great care you would for any of your other important pieces of fishing/boating equipment. As you are aware, batteries are not an inexpensive item.

Unfortunately, they seem to fail at the time we least expect it and definitely when we don’t want them to. Brand new, fresh batteries should have a useful life of about 48 months. It’s critical to ensure your batteries are always fully charged and the electrolyte is topped off so that you get as much of that life as possible from them.

Best,
RK

Question from Annette about Batteries

Hi,
I purchased a Lund Rebel LS recently. I purchased for a friend, a Quest 6-amp battery charger for the trolling motor on the boat. My friend is upset, for he states he will need to invest in another charger for the main battery. I told him I was informed that was not necessary. I need advice on this. I was also informed that you do not need to charge the battery (mercury 60hp). Any information would be greatly appreciated.
thanks in advance
annette

Answer:

Hi Annette –

Thanks for the email and questions regarding your batteries and chargers. It is a bit unclear as to the setup you are describing. Without knowing whether it’s a new or used boat, or too much about the motor/electrical system on the boat, it’s a bit of shooting in the dark.

However, it sounds like the boat has two separate batteries. If that is the case, you are correct in assuming that the battery for the Merc (I assume electric start) needs no charger, as the motor has an alternator that should charge the main battery. That said, the process of how that works can get complicated. The short and simple version is this: if the Merc is only running at low rpm – like idle speed – charging may not take place. The battery only gets recharged properly when the boat is “under way”, going from point A to point B.

On to the trolling motor… Of greatest importance is choosing a charger that is designed for the type of battery that it is intended to charge. The 6-amp charger that you purchased may work just fine, but I don’t know any specifics about it, so I can’t offer an opinion as to how well it will do the job. A good rule of thumb is that the charger should provide a maximum of 20 amps for each 100 amp-hours of rating on the battery, and it should be able to fully charge your batteries within 8 to 12 hours, max. It’s also worth considering a charger that either shuts off or drops to a “float” condition when the battery reaches full charge. The extra money spent on proper batteries and a good charger is well worth it in the long run, or you may find yourself replacing batteries (an expensive proposition) on a fairly regular basis. NOCO produces a wide variety of smart onboard chargers.

My best advice would be to read this article that I wrote for the website. Any of the chargers shown on that page are an excellent choice. It just depends on the system that is powering the trolling motor and the pounds of thrust supplied by the motor. If it is a single deep cycle (marine)/RV battery, I would suggest the Dual Pro RS2 Recreation Series Charger – Two 6A Banks. You can use it for a single battery – the battery for the trolling motor – and in the winter months, connect both the main and the trolling motor battery to it. I bought the Dual Pro 6 Amp/Bank Recreation Series Triple Output Charger last fall and it is the best investment I ever made, as I have two trolling motor batteries and a main. This charger gets the job done on all three over the winter and keeps them as fresh as if they were brand new.

I hope that answers your questions. Best of luck to you and thanks again for writing!

Best,
Rk

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But one quickly learns that, even as one grows older, the learning never stops. Nor should it. Knowledge of batteries is no exception, even as the type and use of batteries continues to evolve.

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Winter Temperatures are the Culprit

So let me share a few additional thoughts with you. It’s a result of what has been one of the most extreme of winters in quite some time here in the Midwest. Yesterday, for example, it was 24 degrees Fahrenheit below zero, and the wind chill was just shy of minus 50!

It doesn’t have a marine battery, but my 2 ½ year-old Nissan Pathfinder not only failed to start the car, it failed altogether… as in dead battery! That battery should have been good for at least 5-6 years. What happened?

In much the same way that extremely high temperatures in the summer months can play havoc with a battery, extremely low temperatures in the cold months can wreak the same havoc on batteries, damaging – if not totally destroying them.

Battery Construction

Marine & RV batteries are only a tad bit different from car batteries; if they are of the same lead-acid variety though, the same risks are prevalent. Why? Because even though improvements are constantly being implemented, lead-acid batteries have changed little since the 1880s.

Marine and RV batteries are generally constructed of several single cells, each producing about 2.1 volts, that are connected in series. A 12-volt battery has 6 single cells connected in series, producing a battery that has a fully charged output voltage of 12.6 volts. This results from flat lead plates that are immersed in a pool of sulfuric acid (aka electrolyte).

Adding water regularly is required for most types of lead-acid batteries in order for them to function properly and remain “healthy”. Keep in mind that these are simply “storage” batteries because they store energy that is transferred to them; it doesn’t last, and the batteries are not capable of making their own.

But let’s talk boats here!

Yep, we will, and I’ll get to that shortly. Here’s the thing. A fully-charged battery (having received energy from another source – say, a charger), when connected, creates a chemical reaction that produces the electricity necessary to do things like start your outboard engine.

That same reaction also produces a substance called lead sulfate, which begins to coat the lead plates in the battery. The process is called sulfation, and is normal during the process of battery discharge. With continued discharge however, the increasing sulfation leads to decreased voltage in the battery, down from the initial 12.6 volts. This results in decreasing ability to produce the “push” of current – amps – out of the battery and into things like the starter on your motor.

Fortunately for us, the lead sulfate can be reconverted back into lead and sulfuric acid, but only if the discharged battery is immediately connected to a battery charger. If that battery is not immediately recharged, the lead sulfate begins to form a type of hard crystals, which cannot be easily reconverted. It can also quickly lead to the demise of the battery.

Can we skip the chemistry lesson, please?

In a relatively wide range of temperatures, their capacity drops about 20% below normal in freezing weather (hot weather can be even more problematical). It can drop to about 50% of normal capacity when temperatures drop below about minus 20 degrees Fahrenheit. At 40% of normal capacity, it is possible a battery can freeze solid, destroying it. The resulting acid that eventually leaks out won’t do much good for your boat, either.

Half of the lesson here is to never let a battery discharge below 80% – at most – of its capacity, or approximately 10.5 volts. The other half is to make certain that, if your battery is not a “factory-sealed” unit, make certain to keep it topped off, on a regular basis, with distilled water. Make certain to always keep it fully charged.

Finally, to the point: keeping a battery healthy

Let’s get directly to the final point. Since we don’t use our boats in the winter – at least not in the upper Midwest where we can encounter frozen water for 5-6 months. During the time our boats have been safely stored away, we tend to forget about the batteries that supply the energy for the fun we enjoy in the warmer months. A weak/seriously under-charged battery can begin to freeze at 32 degrees Fahrenheit, whereas a fully charged battery won’t freeze until the temperature is -80 or more below.

Two questions come immediately to mind:

1. Where is your boat stored?
2. Is your battery stored in the boat?

All batteries will self-discharge, the rate of which depends upon how/where they are stored, and the temperature there.

Let’s assume your battery is rated at 125 Ampere Hours (forgetting for a moment the CCA or Cold Cranking Amps rating). It will self-discharge at a rate of approximately 5 amps per week. Whether stored in the boat or outside of it, if the battery goes into storage on say, November 1, by the end of February – after about 16 weeks without charging, the battery will have lost approximately 80 amps of its 125-amp capacity.

It will now be at less than 40% of its capacity: less than 6 volts! And, although you can’t see it, the battery will have experienced severe sulfation and a vastly reduced life… or perhaps even rendered useless.

At the present cost of new batteries, might it not be worthwhile to clean and add distilled water to your batteries in the fall and connect them to a charger with “Intelligent charging” capabilities over the winter months? Want to keep your batteries healthy? Here’s a link to another article, this one about battery chargers.

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Fully charge them about once a month over the winter. In the spring, they will be ready when you are. Try to keep them off of concrete floors if possible and cover the terminals to help prevent discharge. The last thing you want is a dead battery on the launch ramp on opening day, or a dead trolling motor battery. No matter what kind of battery chemistry you choose, follow these recommendations to get the best performance and longest life from your batteries:

• Stay with one battery chemistry type (flooded, gel or AGM). Each battery type requires specific charging voltages and currents. Mixing battery types can result in under- or over-charging, which may mean replacing all batteries on board at the same time.
• Never mix old batteries with new ones in the same bank. Old batteries tend to pull down the new ones to their deteriorated level.
• Regulate charge voltages based on battery temperature and acceptance. Manually works well. Smart-sensing devices work better to maximize battery life and reduce charge time. Ensure that your charging system can deliver sufficient amperage to charge the battery banks efficiently.
• Keep batteries clean, cool, and dry.
• Check terminal connectors regularly to avoid loss of conductivity.
• Check fluid levels and add distilled water to flooded lead acid batteries when needed. Keep batteries charged; leaving them in a discharged state for any length of time will damage them and lower their capacity; it also reduces lifetime.
• Clean corrosion with a paste of baking soda and water.

With summer now officially here, I hope that most of you have either fished the opener somewhere or are, like me, chomping at the bit to head to the lakes once again. Make sure to check your batteries before you head out.

And when next October rolls around, you will perhaps remember a few things from this article and make sure to take proper care of those very important pieces of equipment: your batteries. For information on charging and chargers, see my article on Charging Your Boat Batteries.

See you On the Lake!
R. Karl

I recommend and use the Dual Pro 15 Amp/Bank Professional Series 2 Bank Charger in my 16′ Lund – Mr. Pike Anniversary Edition!

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The Basics

Although I have found that the subject of batteries and battery maintenance to be a multi-faceted subject that encompasses many different topics, I am going to limit my discussion to a few of the most important “basics”. I want to briefly discuss: the things that will easily destroy a battery, sulfation, and basic maintenance.

Things That Will Destroy a Battery

There are essentially two things that will quickly and easily destroy your battery: either 1) undercharging it or 2) overcharging it. Most of both deep cycle and starting batteries are simply containers for several lead-plates, filled with sulfuric acid (electrolyte).

Simple chemistry dictates that undercharging them will ultimately cause lead sulfate to accumulate on the plates. This will eventually destroy the battery because the normal chemical reaction that should take place will be unable to continue. Overcharging the battery will accelerate the natural corrosion of the plates due to excess electrons being literally boiled out of the electrolyte. Ultimately, the fluid boils away and the plates are exposed to the air, which ruins them.

Sulfation

Have you ever had a battery that seems to work well but “dies” much more quickly than expected? The problem may be a battery that is heavily sulfated. This is often the result of only light use (being discharged by only 15% or so). The sulfuric acid has become concentrated on the battery’s bottom, and sulfate crystals have begun to form. And even though a multi-meter will indicate that all is well in terms of voltage, the capacity of the battery has become severely reduced. Sure, the battery will work just fine, but it will die much sooner than normal.

There are certain types of chargers that have a setting that will temporarily boost the charging voltage for a brief period of time, causing a mixing of the electrolyte, and dissolving the crystals. The process is called equalization and can be done – depending on the manufacturer – about once a year. But beware: this should only be done on wet cell batteries. This same process can ruin other types. And you will need to make sure that you disconnect the batteries from the electrical system to prevent the higher voltage from damaging other equipment.

Maintenance

Batteries have come a long way since the 1960’s. Back then, most – if not all – wet cell batteries were dry to start with. In the storeroom of the gas station at which I worked, there was a large box with a plastic bag filled with electrolyte – sulfuric acid. I found out it was acid the hard way; in filling a battery, I once managed to splash the electrolyte all over my pants. I didn’t realize the power of the stuff until my work pants got washed. They looked as if I had been shot by a machine gun: one leg was nothing but holes! Now there is an incredible variety of batteries that are available for every imaginable use: marine starting & trolling, auto, agricultural, industrial).

They all have at least one thing in common: they need to be maintained to some degree – even the “maintenance free” types. They will lose their electrolyte during normal use and need to be checked; all need to be recharged. Most of us still use the wet cell types for marine applications, although there are essentially three distinct types of lead acid batteries (see “Categories“) manufactured for marine applications, and any one type can be designed and built for either starting or deep cycle applications.

Maintenance-Free and NON Maintenance-Free

As I mentioned, the gelled acid and AGM types are essentially maintenance free since they are sealed. But because of this, be very careful when recharging them. “Smart charger” technology is required, or damage can easily result.

They are also more expensive but do have their advantages. The most important thing for the flooded acid variety is to keep them full. Top them off with distilled water only whenever possible, as minerals in tap water can contaminate the electrolyte.

Keep the terminal clamps clean and free of corrosion; coat them with anti-corrosion spray or even petroleum jelly. Check connections and keep them tight; watch for frayed wires and replace them as necessary. And for a few bucks spent at your local auto parts store, a Battery Hydrometer – used to check the specific gravity of the battery (concentration of acid in it) is a good investment. It is a great way to determine if one of the cells is bad. If the difference in specific gravity is 30 points or more… it’s time to replace your battery!

That’s it for now. Hope to see you on the lake!
rk

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Getting the right battery for the intended task is only part of the story – keeping that battery healthy with the proper charging and maintenance will ultimately ensure that you will have the necessary power when you call for it! Which type of battery you choose is based on your needs (e.g., deep cycle vs. starting), the capacity and lifespan you are looking for, and your budget requirements. So, let’s jump right in!

Wet-Cell or Flooded-Cell Batteries

Generally, the most popular battery and the type most all of us are familiar with, are wet- or flooded-cell batteries. They have several cells inside them that contain a liquid mixture of sulfuric acid and distilled water. They have the advantages of a somewhat lower price, a high number of discharge/recharge cycles (if properly maintained and taken care of), are less likely to be damaged by overcharging and are a bit lighter in weight than comparable AGM or Gel batteries.

The disadvantages are that most have vented, interior-accessible designs, requiring regular inspection. It is up to the owners to make certain the cells are regularly topped off with distilled water. Venting also releases hydrogen gas, meaning the battery compartment must be well ventilated to avoid risk of explosion. Other drawbacks include possible spilling of corrosive battery acid, and a higher rate of self-discharge (6% to 7% per month). Be aware of the fact that wet-cell batteries are more fragile in high-vibration environments (such as boats!).

AGM Batteries

AGM is short for Absorbed Glass Mat, and these batteries feature a dense filling of very fine absorbent fiberglass matting that is saturated with acid/electrolyte and packed tightly between the battery’s plates. The design allows oxygen to recombine with hydrogen gas, thus replenishing the battery’s water content and alleviating the need for refilling. Advantages include being truly maintenance free (except for external cleaning).

They are sealed (which doesn’t allow for gases or acid to leak), can be installed at any angle, and are shock and vibration resistant. They also have a relatively low self-discharge rate (about 3% per month) and can even withstand being immersed in water (I guess that’s in the event your boat gets swamped?).

The biggest disadvantages are that AGM batteries are more expensive, are heavier and are quite sensitive to charging currents and voltages, The result is they are somewhat easy to overcharge, which can ultimately ruin the battery.

Gel Batteries

Gel batteries too, are much like wet-cell batteries in that they are filled with liquid electrolyte. The difference is that the electrolyte is gelled with silicates before the battery is sealed. Like AGM batteries, they use the special technology that eliminates the need for adding water. Advantages? They are maintenance free, sealed, low-temperature tolerant, shock/vibration resistant and have long cycle life. Their most notable advantage is resistance to over-discharge that can damage other battery types.

Gels have an internal self-discharge rate of less than 1 percent per month, so they can be stored for long periods without being recharged. And because they aren’t prone to develop life-shortening plate sulfation when left uncharged, they are a good choice for boaters who often forget to recharge batteries promptly after use. The bad news is that these batteries are often almost twice as expensive as comparable flooded-cell batteries and are also fickle about charging. They require their own special kind of chargers.

Lithium Batteries

Lithium-ion batteries are among the emerging “super battery” technologies. They have a high energy density and are excellent for deep cycle applications. Compared to flooded batteries, lithium batteries deliver savings of up to 70 percent in volume and weight and can offer three times as many charging cycles. They handle incredible amounts of current and therefore can be recharged faster than any other type. Currently in use onboard high-performance offshore racing sailboats and others whose owners demand extreme weight savings and cutting-edge performance, Lithium-ion may be the future… Or maybe not (see the next paragraph). But be prepared and willing to pay premium prices.

Worthy of note, there is a relatively “new kid” on the block in the Lithium category. It is a Lithium Iron Phosphate or: LiFePO4 battery. It has numerous advantages over lithium-ion technologies. In short, it’s much lighter, will tolerate a higher depth of discharge, recharges faster, and will operate at a wider temperature range. However, it is a very expensive option, and it is imperative that you have a “BMS” (battery management system) for your LiFePO4 batteries. But I’ll let you do your own research on this one.

For additional knowledge of batteries, see the other Boat Battery articles.

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One Final Outing

Usually, by the end of October, many of the lakes have “turned over” for the winter. Morning steam rising from the water indicates that the heat energy stored in the lake from the long hours of summer daylight is beginning to return once again to the atmosphere as the lake water begins its annual slumber and ultimate renewal.

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There is perhaps still a little time left for one final outing. Most of you – if not all – have taken your boats out of the water and gotten them cleaned out, “winterized” and ready for next spring’s trek back to your favorite fishing spots. You take very good care of your boats, motors, poles, reels, and other gear inside the boat. But have you really taken the time to consider one of the most important pieces of equipment that you have on board – your batteries?

Most of us take our boat batteries for granted, in much the same manner as we do our car batteries. I used to do that. In fact, I had a car that sat in the warmth of the garage all winter. I thought that an occasional blast from a charger would be enough to do the trick. Boy, was I wrong. And the result was a new battery about every other year – until, after a lecture from my mechanic, I got a little bit smarter about batteries.

So, here are a few things to keep in mind. For starters, there are two basic types of 12-volt batteries:

Cranking or Starting Batteries

These are designed specifically to start your main engine. They are made with thinner and more numerous lead plates inside, allowing for more surface area and thereby providing the quick and massive amounts of energy required for tough starting jobs. While the motor is running, the alternator inside will easily and quickly replenish the used energy.

If your boat is powered by a newer model outboard with sophisticated computers, pumps and sensors, you definitely want to make certain you have enough starting power. It’s a good idea to check your owner’s manual for the recommended MCA (Marine Cranking Amps: a measurement of the number of amps a battery can deliver at 0 ° F for 30 seconds and not drop below 7.2 volts) rating before shopping for a battery; always choose one with a rating equal to or greater than the recommended value.

Deep-Cycle Batteries

These are designed to power on-board electrical accessories such as trolling motors, fish-finders, GPS, radios and the like. In general, these batteries use energy at a much slower rate and often don’t get re-charged until the end of the day.

This deeper and more strenuous discharge is hard on a battery and requires a different design type. The result is a battery with fewer, but much thicker lead plates that will withstand the deep cycling. Deep-cycle batteries can withstand the rigors of several hundred discharge/recharge cycles. Cranking batteries cannot. It’s important to understand that, because of their design differences, substituting one battery type for another is not a good idea.

Using a cranking battery to power a trolling motor will cause the battery to overheat and fail. Besides leaving you without power in a moment of need, purchasing a new battery will definitely be in your future.

Similarly, substituting a deep-cycle battery for a cranking battery will likely not provide the power needed to start your outboard. This could possibly leave you stranded a long way from your dock. As it turns out, the design strengths of each battery type also are their weaknesses in opposite applications.

Having said that, there are dual-purpose batteries that can perform both these functions – to some extent – also are available. Keep in mind however, they will not supply the same starting power as a true cranking battery, nor will they provide the same number of discharge/recharge cycles as a dedicated deep-cycle battery.

Stores such as BassPro, Cabela’s and even Farm & Fleet offer marine batteries for sale. You can also check with local marina or even a nearby auto supply store.

If I have whetted your appetite for more battery knowledge, there are several additional battery articles to assist you…
See……………….

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Charger Types

Most chargers that were designed to charge your car batteries were not designed to charge your boat batteries… for numerous reasons. For one thing, many chargers — especially the less-expensive ones – don’t always completely shut down. And how often do you think that you can remember to unplug that inexpensive charger when things “look about right?” Importantly, buying a low-cost charger with limited charging capabilities will shorten the life of your batteries rather than prolong them. So, what is the best charger to buy in order to keep those expensive marine batteries in top shape?

There are two types of chargers to consider: portable or onboard. Portables are great for many applications. This is especially true when your batteries are at home and/or if they are out of the boat. These chargers also tend to be a bit less expensive than onboard models. The primary disadvantage of portable chargers is that they can be somewhat inconvenient to hook up and switch from battery to battery in the confines of a boat’s battery compartment. And because they are portable, they are more subject to being stolen if you need to use them in places like motel parking lots, boat stalls or other public places.

Onboard chargers, although more expensive, can easily help pay for themselves when it comes to convenience. Since your whole system is already wired, simply plug it in to a 120-volt outlet and let the charger do the work. Because it’s permanently installed, it certainly deters would-be thieves from helping themselves… Perhaps most importantly, on-board chargers are generally more technologically advanced units. They provide the necessary multi-stage switching to manage and maintain a boat’s batteries during charging. I’ll therefore center the discussion around onboard chargers. Specifically, the desired variety is a multi-stage charger.

Multi-Stage Charging

Leaving behind most of the chemistry and physics involved, batteries will do best on a regulated diet of amperes and volts served up in the right amounts. Current battery charging technology relies on computer chips (microprocessors) to do the job. This is done in stages and there are usually three of them: 1) bulk, 2) absorption and 3) float. The chargers engineered for the staging tasks are referred to as “smart chargers”, designed to provide maximum charge benefit with minimum observation on your part.

Bulk Stage

In the bulk stage, which involves about 75-80% of the recharge process, the charger delivers as much current as it is capable of safely doing – up to charger capacity. This is done at a constant rate while the voltage in the battery is increasing.

Note: This ampere amount could be anywhere from 10 -25% of the battery capacity in amp hours and should not raise a wet battery temperature above 125° F, or an AGM or GEL (valve regulated) battery over 100° F.

Absorption Stage

The absorption stage is where the voltage is now constant, but the amperage is tapered and regulated while the battery is “topped off”. This constitutes roughly the remaining 20-25% of the charge, and the battery should now register anywhere from 14.1 volts to 14.8 volts.

Depending on something called a “set point” in the charger, the current must be varied in a precise way in order to hold the voltage constant (at, for example, 14.4 volts). This takes place while the battery absorbs the remaining energy to reach a fully-charged state. (Otherwise, under- or overcharging could occur),

Float Stage

And finally, the float stage is where the voltage is just enough to keep the battery from losing any charge. The charging current has dropped back to almost nothing, allowing the battery voltage to drop back to around 13.5 volts – 13.8 volts. The neat thing is that, since the battery is now fully charged, this “float” mode can be used to maintain a fully charged battery indefinitely.
Smart, multi-stage chargers are designed for faster and fuller charging, which ultimately leads to longer battery life. It also allows more useable capacity from your batteries, less electrolyte loss (in the case of wet flooded batteries), and/or very little chance of over-charging and ruining sealed batteries.

The Right Charger

Opinions differ on the “right” charger. Recommendations for charger size range from 10% up to 25% of the battery’s amp-hour rating. Bottom line? The higher the charger ampere rating, the quicker the recharge time. Recharge time can be approximated by using a fairly simple formula. Divide the number of amp-hours to be replaced by 90% of the rated output of the charger.

How it Works

As an example: Say you have a 100 amp-hour battery that has been discharged by roughly 50 percent. You would therefore need to replace 50 amp-hours. Using a 10-amp charger, take 50 amp-hours and divide by 90% of 10 amps (or 9 amps). This results in an approximate 5.6 hour recharge time.

A deeply discharged battery deviates a bit from this formula, requiring more time per amp-hour to be replaced. A 6-amp charger would require over 9 hours, while a 15-amp charger would take less than 4 hours to replace the 50 amp-hours of charge.

I have a Dual Pro Recreation Series Triple Output Charger in my garage with three 6-amp banks to use at home over the winter (when time isn’t an issue). I connect my one cranking and my two deep-cycle batteries to that charger.

There is also an onboard charger in my boat. That one has two 10-amp banks just for my trolling batteries (two 12-volt batteries for the 24-volt system) that I use over the summer at the dock.

Note: The Recreation Series charger is now known as the Real Pro Series.

In terms of the right charger, the decision is obviously yours. It depends on your needs and how much you want to spend. Higher amperages and more charging banks add more to the price. Also keep in mind that longer charge times require lower currents in the bulk stage and are a bit gentler on the batteries.

If you like quick charge times, I recommend the Dual Pro Professional Series 2-Bank Charger, 15-amp/Bank PS2. Dual Pro Chargers – Professional, Sportsman and Eagle Performance Series is Made in the USA!

Whatever your choice, a good charger is important in maintaining healthy batteries.

See you On the Lake!

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