Marine Batteries: Starters, Deep Cycle, and Dual Purpose


In the world of boating and marine adventures, a reliable and efficient power source is the backbone of any successful voyage. Marine batteries play a crucial role in providing electrical energy for a wide range of applications from starting engines to powering onboard electronics. In this blog post, we will explore the basics of marine batteries, and how to choose the right battery for your application.

What is a marine battery?

Marine batteries are a type of battery designed to provide power for marine applications, such as boats, yachts, and other watercrafts. They have three types based on their jobs: starting batteries, deep cycle batteries, and dual-purpose. The starting battery ensures reliable engine ignition, while the deep cycle battery provides a steady power supply for extended use of electrical systems and appliances on board. Dual-purpose marine batteries are designed to serve both starting and deep cycle purposes.

Boat driving across the water

Starter Batteries

Marine starter batteries, also known as marine cranking batteries or marine engine start batteries, are a type of lead-acid battery specifically designed for the purpose of starting boat engines. They are engineered to deliver high-cranking amps (CA) and cold-cranking amps (CCA) for quick engine ignition.

Cranking amps is a measure of a battery’s ability to deliver a burst of power at 32°F (0°C) for 30 seconds while maintaining a minimum voltage. CA is commonly used to assess the battery’s starting power in relatively mild or moderate climates, where the temperatures are not extremely cold.

Cold Cranking Amps, on the other hand, are a more stringent measure of a battery’s starting power. It is defined as the maximum current a battery can deliver at 0°F (-18°C) for 30 seconds while maintaining a minimum voltage. CCA is crucial for cold weather starting, where the engine oil may be thicker, making it more challenging for the engine to turn over. For more information on cold cranking amps check out our blog post, “What are CCAs”.

Lithium Marine Battery Group 31

Deep Cycle Batteries

Deep-cycle marine batteries are specifically designed to provide a steady and sustained power output over an extended period, making them ideal for applications that require continuous power delivery. Unlike starting batteries that are optimized for short bursts of high current to start engines, deep-cycle marine batteries are built with thicker lead plates to withstand repetitive deep discharging and recharging without damage.

These batteries are commonly used to power various electrical systems and appliances on boats, such as lights, trolling motors, fish finders, radios, and refrigerators. Deep-cycle marine batteries are crucial for boating activities that demand a reliable and long-lasting power source, ensuring that boaters can enjoy their time on the water without worrying about power interruptions.

Dual Purpose

Dual-purpose batteries aim to provide a balance between the characteristics of cranking (starting) batteries and deep-cycle batteries. These batteries are engineered to deliver the high burst of power needed to start an engine while also being capable of providing a moderate amount of sustained power for running onboard electronics and accessories.

Many deep-cycle marine batteries on the market today are designed with dual-purpose capability. If you have a smaller boat with a less demanding engine, a quality dual-purpose deep-cycle marine battery might be sufficient to start the engine and power accessories. However, for larger boats with more powerful engines or if you have a lot of onboard electronics and accessories, it’s generally recommended to use a dedicated cranking battery for engine starting and a separate deep cycle battery (or batteries) for accessory power.

Marine Sealed Lead Acid (SLA) Battery Group 31

How are marine batteries different?

Marine batteries have specific characteristics to withstand the unique challenges of the marine environment, such as constant motion, vibration, and exposure to moisture. They are engineered to combat the vibrations and shocks experienced on boats, especially during rough waters or high-speed travel. This is achieved through improved construction and internal components that secure the battery’s plates and prevent damage from vibration. Due to the potential risks associated with marine environments, marine batteries often have additional safety features. For example, some marine batteries are equipped with spark arrestors to prevent explosions in case of an accidental spark during charging.

Additionally, marine batteries are designed to resist corrosion caused by exposure to saltwater and other corrosive elements found in the marine environment. They typically use materials that are more resistant to corrosion, such as lead alloys. Lastly, marine batteries can come with different terminal types and sizes to accommodate various boat setups and electrical systems. For example, some marine batteries have specialized terminal designs to prevent accidental short circuits or to enable quick-connect features.

Boat driving through a tunnel

What size marine battery do I need?

Marine batteries come in various sizes to accommodate different power requirements and fit specific battery compartments on boats. The size of a marine battery is typically expressed in terms of group sizes, with numbers or letters used to identify the different sizes. Larger group sizes generally offer higher capacity and are suitable for applications with higher power demands, such as powering multiple electronics and accessories. Smaller group sizes are ideal for smaller boats or those with lower power requirements. Choosing the right marine battery size ensures optimal performance, efficient space utilization, and reliable power supply for various applications during boating adventures. You can learn more about marine battery sizing here.

Lithium or Lead Acid?

Marine Lithium Battery Family Group 31

Lithium batteries offer a host of significant advantages that make them an excellent choice for marine applications. One of their key strengths lies in their exceptional energy density, allowing them to store more power in a smaller and lighter package compared to traditional lead-acid batteries. This weight reduction not only enhances boat performance but also optimizes fuel efficiency and handling. Another prominent advantage is their long cycle life, enduring thousands of charge and discharge cycles, far outlasting lead-acid batteries. This longevity ensures boaters can rely on lithium batteries for extended periods without frequent replacements, providing a more reliable power source for their marine adventures.

Additionally, lithium batteries boast a higher charge efficiency, meaning they can absorb and store energy more efficiently during charging, reducing downtime and maximizing time spent on the water. Furthermore, lithium batteries, despite their higher upfront cost, prove to be a more economical and efficient choice in the long run. You can learn more about the benefits of lithium here.

Marine Batteries Lithium VS SLA

While lithium batteries are considered the optimal choice for marine applications, lead-acid batteries offer their own set of advantages. They have a lower upfront cost, providing a budget-friendly option for boaters looking to power their vessels without breaking the bank. Another advantage is their safety and reliability. They are well-established, as they have been used in the marine industry for many years, building a proven track record. Lastly, lead acid batteries are well-suited for starting applications, as they have no over-current protections. Check out Battery Universities’ article, “Can the Lead-Acid Battery Compete in Modern Times?’ for more advantages of lead acid.

Sealed Lead Acid (SLA) family image

How long do marine batteries last?

The lifespan of marine batteries varies depending on their type. Starting batteries, designed for quick bursts of high current, typically last around 3 to 5 years. Deep cycle batteries, engineered for sustained power delivery, can endure between 2 to 4 years when well-maintained. Lithium marine batteries, on the other hand, can last 10 to 15 years!

Frequent use and deep discharging can put additional stress on lead acid marine batteries, leading to faster wear and shorter lifespans. Properly managing discharge levels and avoiding over-discharging can significantly extend battery life. Additionally, correct charging practices are crucial for battery longevity. Overcharging or undercharging can harm marine batteries, reducing their service life. Utilizing smart chargers that deliver the right charging voltage and current based on the battery’s capacity and state of charge helps preserve the battery’s health. Lastly, regular maintenance, including cleaning terminals and protecting batteries from extreme conditions, is essential to extend their life in this challenging setting.

How should a marine battery be stored?

Choose a storage location that is cool, dry, and well-ventilated. Avoid exposing the battery to extreme temperatures or direct sunlight, as both can accelerate the battery’s degradation. A stable storage environment helps preserve the battery’s performance and protects it from unnecessary wear. Before storing the marine battery charge the battery according to the manufacturer’s recommendation. To learn more, check out Battery Universities’ article, “How to Store Batteries”.

Boats on a dock


In conclusion, understanding the basics of marine batteries is essential for making an informed decision that aligns with your boating needs. Marine batteries are built with unique features to endure the harsh environment at sea. Both lithium and lead acid battery types have their advantages and considerations for marine applications. When choosing between the two, consider factors such as power requirements, available space, weight capacity, and budget constraints. Careful battery selection ensures that your marine adventures are powered efficiently and reliably, allowing you to embark on memorable journeys with peace of mind.

Categories: Blog, Batteries, Lithium, PowerSport

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