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Dual Purpose agm batteries vs. Deep-Cycle Marine Batteries

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Are Dual Purpose Batteries Better Than Conventional Flooded Lead Acid?

Whether you rely on a multiple-battery system or a single battery for your work truck, a reliable battery is essential equipment to keep you on the road and operating all the electrical accessories you need. For the best experience, there are some questions you should ask. Are all batteries ideal for multiple-battery systems? Should you use conventional flooded lead acid batteries? What if you can only use one type of battery—which one is best?

Generally speaking, the right battery is the one you can depend on. That means choosing a battery that meets the requirements of the application, performs well and lasts a long time.

While the price of a conventional flooded lead acid battery may appear to be less expensive  upfront, in the long run it can end up costing more. Let’s take a closer look to understand some of the critical differences between dual purpose and conventional flooded lead acid batteries.

27M-580 12v92ah dual purpose agm battery
27M-580 12v92ah dual purpose agm battery

Conventional Flooded Lead Acid Batteries

The basic technology of conventional batteries has been around for more than 150 years, and  continue to be widely used, although perhaps, not best suited for every application.

Sometimes referred to as “starter batteries”, these batteries are designed to deliver a large burst of power for a short time, as in starting an engine. The battery is then recharged by the alternator in the vehicle. They consist of a plastic outer case and cover that houses lead plates surrounded by liquid electrolyte (dilute sulfuric acid). Unlike a deep-cycle battery, starting batteries are designed for only shallow cycles. Deep cycling can significantly shorten its life.

All batteries self-discharge when not in use. Flooded lead acid batteries generally have a higher rate of self-discharge and are more dramatically affected by extremes in temperature.

Conventional flooded lead acid batteries also require more maintenance, like water addition, and terminal cleaning to remove any corrosion. Typically, these batteries are somewhat less robust as the cases and covers are not designed for the extreme shock and vibration experienced in commercial vehicle service. Cracks in the cases can cause acid to leak from the battery and vibration can damage internal components. Battery performance can also be dramatically affected by extreme temperatures.


Dual Purpose Batteries

Dual purpose batteries are ideally suited for applications that require both strong cranking power and low-amp draw (cycling) service to meet the extended auxiliary power needs of electrical accessories. Among this class of battery, Absorbed Glass Mat (AGM) sealed batteries are a top performer.

Inside AGM batteries, positive and negative lead plates are separated by an absorbent glass mat that holds the electrolyte, rather than being immersed in electrolyte. The plates and separator are tightly compressed in cells and held within a durable plastic case. This extremely tight compression limits “shedding” of plate material that happens during battery cycling and produces significantly longer battery life. In addition, the compression serves to lower internal resistance and maximize power output, improving performance in colder temperatures.

Deep cycling, dual purpose AGM batteries charge up to five times faster and offer a depth of discharge of 80 percent, compared to flooded lead acid batteries that offer 50 percent for the same rated cycle life.

Sealed AGM batteries experience very little water loss and recombine most gasses within the battery. However, the design of these batteries also features a valve that releases any excess pressure that might occur from minor gassing during charging.

31M-825 12v105ah dual purpose agm battery
31M-825 12v105ah dual purpose agm battery

Review and Compare

AGM dual purpose batteries offer many unbeatable advantages over conventional batteries, and some of the key differences are outlined below. Be sure to evaluate how the benefits support your work truck demands:

  • Excellent starting capability
  • Deep cycle performance
  • More starts per battery, up to three times longer battery life
  • Low self-discharge rate
  • Recharges up to five times faster
  • Low maintenance
  • Minimizes surface corrosion
  • Excellent cold weather performance
  • Less prone to sulfation and grid corrosion
  • More durable construction, vibration resistant
  • Non-spill, safer to handle
  • Special valves to protect battery lifespan

When it comes to choosing a battery for your work truck, never was the old saying, “you get what you pay for,” truer. Choosing a quality dual purpose battery will more than pay back the initial cost difference when compared to a conventional flooded lead acid battery, in maintenance, performance and battery life. Always be sure to follow the manufacturer’s guidelines for battery care and handling, and direct any questions to your battery professional.

Dual-Purpose vs. Deep-Cycle Marine Batteries

Whether you’re looking to take your bay boat out for a quick fishing trip in the intracoastal waters, or you have a large center console boat that you’re planning to take off shore for an overnight trip, that boat lives and dies at the whims of its batteries. The batteries on your boat may be similar to batteries that you’re used to already, such as ones that you find in a car, but they also have specific challenges that you need to consider when using them for marine purposes.

Another thing to consider when thinking about batteries for your boat is that there are multiple types of batteries, and they are not necessarily interchangeable. What you plan on doing in your boat might completely change the kind of battery you need, and you’ll likely need more than one kind unless you plan accordingly.

Batteries for starting your boat are very different than deep-cycle batteries, which themselves provide a different service than a dual-purpose battery will. For this article, we’ll focus on dual-purpose versus deep-cycle marine batteries. While there is a decent amount of overlap between the two, each has unique strengths as well as things to keep in mind as you use them. By the end, you’ll be able to tell which kind of battery is right for you.

What Is a Deep-Cycle Marine Battery?

The name of deep-cycle batteries gives a small hint as to how they’re supposed to work. They’re specifically designed for light usage over long periods of time. The deep-cycle terminology also refers to how often they can be discharged and recharged.

If you run an electric trolling motor or have a lot of electronic systems onboard your boat, deep-cycle batteries are an essential part of your boating equipment. Having a deep-cycle marine battery that you rely on means you’ll also need a separate starting battery to kickstart the engine when you first turn your boat on.

What Is a Dual-Purpose Marine Battery?

As the name suggests, dual-purpose marine batteries offer the abilities of both major kinds of batteries all in one unit. Rather than having a starting battery and a deep-cycle battery, dual-purpose batteries can handle both jobs at the same time. Boats with less room for larger or more numerous batteries can benefit from having a dual-purpose marine battery instead.

Depending on the battery’s construction and materials, you might find that they don’t perform as well as batteries with a more specific purpose in mind.


What’s a Dual-Purpose Battery, and Why Should I Care?

What’s a dual-purpose battery you say? Well, it’s only one of the most important types of batteries in existence! A dual-purpose battery fills a very important application niche, without it, life for boaters, off-roaders, car audio enthusiasts, and many others would just be a lot less fun. And of course, emergency services and first responders would be sad too, when they can’t rely on their equipment, the results can potentially be tragic. But it isn’t just boats and firetrucks that need a resilient battery, today even standard cars with multiple computers need a more robust battery to keep up.

It all ‘Started’ with an Engine

Visualize the earliest automobiles, more closely related to a horse-drawn carriage than a modern automobile.  The earliest automobiles had to be cranked by hand to start them, and often used kerosene lanterns for light (sort of scary). As the story goes, technology advanced quickly to incorporate a starting motor and electric lights, which of course required a battery. This battery only needed to get the car started and handle the lighting for a short amount of time before it could simply be recharged. The starting battery was born and is still relied on by gazillions of vehicles around the world. It is well suited to do its simple task, start the engine.

As time went on, technology has been added to our technology. Our vehicles, whether on water or land, whether for pleasure or commercial purpose, have become something much more than engine-based propulsion. Extra lighting, computers, comfort controls, visual displays, accessory charging, the power demands have made it so the starting battery is no longer enough, not nearly. Ok, so we have large electrical loads, why not just use a deep-cycle battery like a golf cart would use? That is possible, but not ideal as we’ll see.

Go with a deep-cycle and call it good.

Ah, yes, now we’re getting into the weeds, the really special side to our beloved Dual-Service battery comes out when we compare it to a true deep cycle battery. A deep-cycle battery’s core competency is running electrical loads for long periods of time. It is less capable when it comes to starting an engine, because it wasn’t designed with this purpose in mind. The thick plates inside a deep cycle battery don’t have the surface area to provide the large amp draw that cranking requires as efficiently as a starting battery. And there’s another drawback to using a deep-cycle battery, the thick plates take much longer to recharge. Once the engine is fired up and sending current to the battery, the uptake of energy is slower because of those thick plates.

Advantages Of A Dual-Purpose Marine Battery

More Space

Space on a boat is as valuable as a glass of milk with a chocolate-chip cookie. Many boaters opt for a dual-purpose marine battery setup when they have limited room on board.

Less Weight

Need to cut back on your weight a bit? No, that’s not a jab at your waistline! A dual-purpose marine battery is a great weight solution. You can reduce your boat’s weight by using less batteries.

Less Money

Buying one dual-purpose battery covers the work of two batteries. So it’s basically two for the price of one, roughly speaking.

dual purpose marine battery
dual purpose marine battery

Lead-acid Battery Topic: | Feature | | Applications | | Related Products || 31M-720|


Faq for Dual Purpose Marine Battery

Are dual-purpose marine batteries any good?

Marine Dual-Purpose Batteries combine the performance of a starting with deep cycle battery, making them a viable alternative for smaller boats with limited space. They can execute the functions of both beginning with a deep cycle battery, although they aren’t as efficient as individual batteries.

What’s the difference between a dual-purpose battery and a deep cycle battery?

Deep cycle batteries, for example, are designed to tolerate multiple discharges and recharges, whereas cranking batteries are not. As a result, a dual-purpose battery falls somewhere in the middle. Many are unable to withstand entire discharges (discharge beyond 50 percent of usable capacity).

What is the life expectancy of a dual-purpose battery?

Here’s how it’s done… When it comes to boat batteries, how long do they last? Depending on how well you care for your marine batteries, they can last anywhere from 2 to 5 years.

Is it possible to utilize a dual-purpose battery to power a trolling motor?

A dual-purpose battery can start and turn over the engine while also delivering enough energy to keep your trolling motor running constantly. Dual-purpose batteries, as the name implies, can be used for both functions. When combined with a trolling motor, they will deliver outstanding results.

What is the difference between a Marine Dual Purpose Battery and a Marine Single Purpose Battery?

Traditional deep cycle and starting batteries are both performed by dual purpose marine batteries. Over the course of a full day of fishing, these batteries should be able to start the outboard engine and provide enough juice to run the equipment.

What is the best way to charge a dual-purpose marine battery?

Check to see if your 12-volt constant current charger is switched off. Connect the red, positive terminal to the positive side and the negative, black terminal to the negative side. Bulk charging is the first phase of charging, during which you keep the charger amperage constant while the voltage of your battery rises.

What is the best way to store a marine battery for the winter?

Remove the batteries and store them somewhere cold and dry where they won’t freeze. (It’s best to use on wood surfaces in garages or storage buildings.) Ideally, charge batteries in stages or once a month. Self-discharge is avoided, and the lifespan is extended.

Is it possible to use a trickle charger with a marine battery?

Because trickle chargers do not generate excessive heat, they are ideal for maritime batteries. The battery heats up during a typical charge.

Is it AGM or gel in a deep cycle marine battery?

One crucial aspect to remember is that Lead-Acid batteries are employed in all deep cycle applications. This covers ordinary flooded, gelled, and sealed AGM batteries. They all use the same chemistry, but the plates, for example, are built differently.

What amperage should my boat battery be charged at?

Charge at a voltage of roughly 14.6 volts at a rate of up to 20% to 40% of the battery capacity in amp hours (gel: 14.1 volts). A 200 amp-hour battery, for example, would be charged at 40–80 amperes.

Is it possible to utilize a lithium battery on a boat?

Yes, lithium batteries are suitable for marine and boat use. Because lithium batteries are sealed, moisture and even a small amount of water splashing on them will not affect them. In addition, most lithium batteries include a battery system built in (BMS).

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