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Marine Batteries: Deep Cycle VS Cranking & Dual-Purpose Battery

Mike Smith
Mike Smith
—
10/05/2023

When it comes to powering a boat, selecting the right battery is critical for both performance and reliability. Three of the most common types of marine batteries are starting, dual-purpose and deep-cycle batteries. Each serves different functions and is designed to meet specific power needs.

In this guide, we’ll break down the differences among starting, dual-purpose and deep-cycle marine batteries, helping you decide which is the best fit for your vessel.

Part 1: Understanding Marine Deep Cycle Battery

The term "deep-cycle" offers a clue about how these batteries function. They are specifically engineered for sustained, low-level power output over extended periods. The "deep-cycle" designation also refers to their ability to endure repeated discharges and recharges.

If you operate an electric trolling motor or have multiple electronic systems on your boat, deep-cycle batteries are essential. However, because they are designed for powering electronics rather than starting engines, you’ll need a separate cranking battery to provide the burst of power necessary to start your boat.

starter vs deep cycle battery

1.1 Traditional Deep Cycle Marine Battery Design Features

Deep cycle marine batteries are designed to provide reliable power for an extended period of time. These batteries are built differently than starting batteries because they are designed to deliver long-lasting power at a lower voltage. Below are some of the key design features of traditonal lead acid deep cycle marine batteries:

1. Thicker Plates

Deep cycle batteries are designed with thicker plates compared to starting batteries. The thicker plates offer a greater surface area for active material and more room for the electrolyte, thus allowing the battery to deliver more sustained power over a longer period.

2. More Active Material

The active material in the plates of deep cycle batteries is denser than that in starting batteries. This means that there is more active material per unit area, which allows the battery to have a longer lifespan with more cycles of discharge and recharge.

3. Low Discharge Rates

Deep cycle marine batteries are designed to deliver low discharge rates, enabling them to provide continuous power for long periods of time. This feature is crucial for powering accessories like trolling motors, fish finders, and other electronics that require constant power over an extended duration.

4. Thicker Separator

Deep cycle batteries have a thicker separator which is designed to prevent short circuits between the positive and negative plates. This separator helps to minimize the risk of internal damage to the battery due to physical shocks or vibration typically experienced on board boats.

5. Heavy Duty Construction

Deep cycle marine batteries are designed to handle rough marine conditions. The construction features include enhanced resistance to vibration, shock, and corrosion. Marine batteries are also designed to be spill-proof to avoid damage to the boat or the environment in case of leaks.

marine deep cycle battery

6. Multiple Charging Options

Most deep cycle marine batteries can be charged through multiple options like on-board chargers, solar panels, or even wind turbines. They can handle trickle charging and bulk charging too, depending on the charging source available. Read on 3 reliable ways to charge LiFePO4 lithium marine deep cycle batteries. 

1.2 Type of Marine Deep Cycle Battery

1. Lead-acid Battery

Lead-acid batteries are the most widely used type of deep-cycle battery and come in two varieties: flooded lead-acid (FLA) and sealed lead-acid (SLA). FLA batteries require regular maintenance, as the electrolyte levels must be checked and replenished periodically. In contrast, SLA batteries are maintenance-free.

lead acid battery

However, lead-acid batteries have several drawbacks.

First, they have the lowest C-rating among the battery types discussed, which means they cannot be charged or discharged quickly without risking damage.

Additionally, they require more advanced chargers capable of providing equalization charges to maximize their lifespan. Improper maintenance can lead to sulfation, and these batteries cannot be left in a partial state of charge or discharged below 50% of their rated capacity, significantly reducing their usable power.

Moreover, lead-acid batteries are sensitive to positioning, and submerging them can release hazardous chlorine gas. They need constant float charging, even when not in use, and periodic water refilling is necessary.

Lastly, ensuring proper ventilation in the battery compartment is essential to prevent potential explosions caused by the release of hydrogen gas during charging.

In conclusion, while lead-acid batteries remain a popular choice for deep-cycle applications due to their affordability and widespread availability, they come with several limitations.

  • The need for regular maintenance.
  • Sensitivity to charge and discharge rates.
  • Reduced usable capacity make them less convenient than more modern battery technologies.
  • Safety concerns—such as gas emissions and the requirement for proper ventilation—add further challenges.

For those seeking more efficiency, reliability, and lower maintenance, exploring alternatives like lithium-ion batteries may be a better long-term solution.

2. Lithium Battery

Lithium-ion (Li-ion) batteries are gaining popularity in the deep cycle battery market due to its various advantages over the traditional lead-acid battery. Li-ion batteries typically have higher energy densities, longer lives, and are lighter in weight compared to lead-acid batteries; making them ideal for marine applications. The only type of lithium ion battery approved for marine use is currently the lithium iron phosphate (LiFePO4) battery.

LiTime provides lithium deep cycle battery for trolling motor, features with

  • Innovative moisture-proof design
  • Salt-spray resistance for heightened durability
  • Advanced low-temperature cutoff protection for safe charging

lifepo4 lithium marine deep cycle batteries

LiTime 12V 50Ah TM Lithium Marine Trolling Motor Bluetooth Battery

Part 2 Understanding Marine Starting Battery

Marine starting batteries also called cranking batteries are designed to provide a burst of power for a short period of time at a higher voltage. These batteries are used to start the engine of the boat, and once the engine is running, the alternator takes over to provide power to the boat's electrical system.

2.1 Features of Marine Starting Batteries

1. High Cold Cranking Amps (CCA)

Cold Cranking Amps (CCA) is a measure of a battery's ability to start an engine in cold conditions. Marine starting batteries are built with a high CCA rating to ensure they can deliver the rapid burst of energy needed to start an engine, even in cold or challenging conditions.

marine starting battery cca

2. Short Burst Power

Marine starting batteries are designed to provide a strong jolt of power in a short timeframe, usually lasting only a few seconds. This high discharge capability ensures the engine starts quickly and efficiently.

3. Durability for Marine Conditions

These batteries are built to withstand the harsh environments of the marine world, including exposure to vibrations, humidity, and saltwater. They are encased in rugged, corrosion-resistant materials to protect them from these conditions.

4. Quick Recharge

After providing the energy to start the engine, marine starting batteries recharge quickly, ensuring they are ready for the next start without requiring a long charging period.

5. Limited Deep-Cycling Capability

Marine starting batteries are not intended for deep discharges or powering electronics for extended periods. Repeated deep cycling can cause permanent damage, shortening the battery’s lifespan. They are optimized for starting engines, not for providing sustained power.

6. Maintenance Requirements

Depending on the type (flooded lead-acid vs. sealed), marine starting batteries may require periodic maintenance, such as checking and refilling electrolyte levels. However, sealed batteries (SLA or AGM) are maintenance-free, offering a more convenient option for boaters.

7. Compact Design

These batteries are generally compact and lightweight compared to deep-cycle batteries, making them easier to install and fit in boats with limited space for battery storage.

2.2 Types of Marine Starting Battery

There are 3 main types of marine starting batteries:

1. Flooded batteries:

Flooded batteries, also known as wet-cell batteries, are the most common type of marine starting battery. They use lead-acid chemistry and require maintenance, which includes adding distilled water to the cells periodically to replenish the water lost during the charging process. Flooded batteries are typically cheaper than other types of marine batteries.

Pros:

  • Low initial cost.
  • Widely available and familiar technology.
  • Reliable performance for starting engines.

Cons:

  • Requires regular maintenance (checking and refilling electrolyte levels).
  • Must be installed upright to avoid spills.
  • Releases gases during charging, requiring proper ventilation.

2. Absorbed glass mat (AGM) batteries

AGM batteries are maintenance-free and have a longer service life than flooded batteries. They are designed with a glass mat that absorbs and holds the battery's acid electrolyte, so there is no need to add water or maintain the electrolyte level. AGM batteries are also vibration-resistant and can discharge at a higher rate than flooded batteries, making them a good choice for high-performance boats. However, AGM batteries are more expensive than flooded batteries.

Pros:

  • Maintenance-free—no need to refill electrolytes.
  • Spill-proof and can be mounted in various positions.
  • More resistant to vibration and shock, ideal for harsh marine environments.
  • Faster charging and better performance in cold weather.

Cons:

  • Higher upfront cost than flooded lead-acid batteries.
  • May have a shorter lifespan when frequently deep-cycled.

3. Lithium batteries

Lithium batteries represent the latest in marine battery technology, offering several advantages over traditional flooded and AGM batteries. Lithium marine starting batteries are lightweight, compact, and provide superior cranking power, ensuring quick and reliable engine starts.

They boast a much longer lifespan—often exceeding 2,000 cycles—making them a cost-effective long-term investment despite their higher initial cost.

Additionally, lithium batteries recharge rapidly, require no maintenance, and are not affected by deep discharges, allowing them to deliver consistent performance even under demanding conditions. Their resilience to extreme temperatures, high energy density, and low self-discharge rate make lithium batteries the top choice for boaters seeking the best in marine starting power.

Pros:

  • Significantly lighter than lead-acid batteries, reducing boat weight.
  • Longer lifespan—often 3-5 times longer than traditional lead-acid batteries.
  • Fast charging times and higher energy efficiency.
  • Can handle deeper discharges without performance loss.

Cons:

  • High initial cost.
  • Requires a compatible charger.
  • Less available in the market compared to lead-acid batteries.

LiTime 12V 20Ah Marine Starting battery boasts an impressive over 5000 cranking times, utilizing EV-grade starting LiFePO4 cells. With IP67 water & dust-proof protection, it is upgraded with a low-temperature cut-off function to ensure safe use in low-temperature environments.

litime marine starting lithium battery

Part 3 What is Dual Purpose Marine Batteries

Dual purpose marine batteries are a type of battery that is designed to serve two functions - starting an engine and powering electrical components on a boat. They are typically a hybrid of a starting battery and a deep-cycle battery, combining the high cranking power of a starting battery and the deep cycling capabilities of a deep cycle battery. Dual purpose marine batteries are used by boat owners who want a single battery to handle both starting the engine and powering electrical systems. This eliminates the need to have separate batteries for each purpose, which can save space and reduce complexity.

marine dual-purpose lithium batteryy

LiTime 12V 140Ah Dual Purpose Marine Battery

While they are not the best option for either starting or deep cycling, dual-purpose marine batteries offer a good compromise between the two.

Generally, dual-purpose marine batteries are most suitable for smaller boats, such as fishing boats, ski boats, and small pleasure crafts that do not have high electrical demands and do not require a high cranking power to start the engine. This includes boats that have basic electrical systems, such as lights, fish finders, and radios.

However, if the boat has a larger electrical system, such as a refrigerator, air conditioning, or other high-demand electrical components, a dual-purpose marine battery may not be sufficient. In such cases, a dedicated deep cycle battery is preferred. Additionally, if your boat has a high horsepower engine that requires a lot of cranking power, then a dedicated starting battery would be the best choice.

Therefore, it is essential to carefully evaluate your boat's need before selecting a marine battery. If you have any concerns or need help selecting the right battery for your boat, please visit our website or consult a professional marine electrician.

Part 4 Maintenance of Marine Batteries

Both marine starting and deep cycle batteries require regular maintenance to ensure their longevity and optimum performance. Following are some tips on maintaining your marine batteries:

  1. Clean the battery terminals regularly to avoid corrosion.
  2. Check the fluid levels regularly in flooded batteries and top them up with distilled water if necessary.
  3. Charge your batteries with onboard chargers or smart chargers designed for marine use.
  4. Store your batteries in cool and dry places during the offseason.

If using LiFePO4 batteries, it would be less likely to get terminal corrosion, learn How to Maintain LiFePO4 Lithium Battery.

FAQS about Deep Cycle and Cranking Battery

1. Can I use a deep-cycle battery to start my boat engine?

No, deep-cycle batteries are not designed to provide the high burst of power needed to start an engine. You will need a cranking or dual-purpose battery for that.

2. How long do marine batteries last?

The lifespan of marine batteries varies based on use, type, and maintenance. A well-maintained lead acid deep-cycle battery can last up to 5-6 years, while a dual-purpose battery may last 2-3 years under heavy use.

Lithium batteries can last up to 10 years.

3. Can I mix dual-purpose and deep-cycle batteries on my boat?

Yes, you can use different batteries for different purposes. For instance, you could use a deep-cycle battery for electronics and a dual-purpose battery for starting and auxiliary power.

By understanding the differences between dual-purpose and deep-cycle marine batteries, you'll be equipped to make the best decision for your boating needs, ensuring you have the power you need for both your engine and electronics while out on the water.

Conclusion

We have introduced the 3 types of batteries in detail, if you are looking for the deep cycle battery for your marine, lithium Iron Phosphate (LiFePO4) batteries are an excellent choice due to their efficiency, long lifespan, and ability to withstand deep cycle usage.

marine deep cycle battery

Mike Smith
Mike Smith
Mike Smith is a marine energy expert with 15+ years of experience and a Master’s in Electrical Engineering from Stanford. Passionate about lithium battery integration, he also enjoys sailing and exploring coastal waters in his free time.

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