What is a Marine Battery: Definition, Types & Technical Specifications

Boats usually have different batteries on them for various applications. Each of these types is critical to the boat’s function. Choosing the wrong battery or using it inappropriately can cause the boat to come to a standstill in the middle of use.

Therefore, it becomes vital to understand what is a marine battery. This article will have an in-depth discussion on the same. You will also learn about the different types of marine batteries, their purpose, specifications, and other important information.

What is a Marine Battery?

A marine battery is a specially designed power storage device for marine applications, such as boats and yachts. It features a robust build to withstand harsh aquatic conditions, including moisture, salinity, and constant motion.

Marine batteries come in two main types: starting batteries, which supply a high current for short periods to start an engine, and deep-cycle batteries, designed for consistent, long-term energy output to power onboard appliances and systems.

Their durability and efficient energy supply make marine batteries a crucial component in ensuring safety and comfort during maritime activities.

Different Marine Batteries

Different Marine Batteries

Commonly, boats have two different types of batteries. Each of the two boat batteries has specific purpose. These different boat batteries are:

Starting Battery

The starting battery starts the boat. It is also known as a cranking battery. It provides a high surge of current over a very short time. The job of cranking battery is finished once the boat is started. The boat’s engine alternator recharges this battery during the boat operation.

Deep Cycle Battery

Deep cycle battery powers the different appliances on the boat. These appliances can be lights, electric ovens, refrigerators, navigation systems, or any other electric gadget. A deep cycle battery can also run the trolling motors present on a boat. Generally, the term ‘marine battery’ refers to deep cycle batteries.

Hybrid Battery

A hybrid battery is a single unit that functions as a starting battery and a deep cycle battery. Therefore, they are also called dual-purpose batteries. Dual-purpose batteries are used in smaller areas and on a tighter budget. While they combine the purpose of starting batteries and dual-purpose batteries, they don’t have a matchable performance.

This is why dual purpose marine batteries are used as the last resort. It is always better to have two different batteries than marine dual-purpose batteries if possible.

Why Do Boats Have Two Batteries?

Boats have two batteries because marine starting batteries and deep cycle batteries have different specifications. Starting batteries have thinner plates for larger surge currents. On the other hand, a deep cycle battery has thicker plates for low, prolonged current. These batteries are not interchangeable. This creates the need to have two separate batteries on the boat.

Some boats replace the two different batteries with a single dual purpose battery. However, dual purpose batteries are significantly underpowered and cannot fulfil the needs of most users.

Marine Battery Specifications

Marine Battery Specifications

Buying or using marine batteries requires a basic understanding of certain battery specifications. These specifications can help in battery comparisons, troubleshooting, and choosing the right battery.

Battery Capacity

Battery capacity is measured in Ampere hours (Ah). It is the primary criterion for these batteries. It provides information on how much power the battery can store and provide. A higher battery capacity means a longer running time or the ability to power larger loads for the same duration.

The appropriate battery capacity can vary depending on the boat’s load. The load is the different appliances like lights, bilge pumps, GPS, radio, trolling motors, etc. These appliances are often rated in KW instead of Amperes. Therefore, converting the battery capacity to KWh can be useful.

This can be done by multiplying the battery capacity with the load voltage. The load voltage in marine applications is usually 12V. Therefore, a 100 Ah battery will provide a power of 1200 Wh or 1.2 kWh.

This means the battery can run a load of 120 W for 10 hours. To calculate the running time for your boat appliances, add their individual load rating.

Cold Cranking Amps

Cold cranking amps (CCA) refer to how much current the battery can deliver in cold conditions. This parameter is important for cranking batteries that start the engines. CCA rating is done at -18 C (0 F) for 30 seconds.

A better CCA rating means a higher battery performance in cold conditions. If your boat operates in colder areas, the CCA rating of the battery can be important.

Marine starting batteries can often have a Marine Cranking Amps (MCA) rating instead of a CCA rating. MCA is very similar to the CCA rating. However, MCA rating is tested at 0 C (32 F) instead of -18 C. To convert a CCA rating to an MCA rating, a common method is to multiply it by 1.25.

Reserve Capacity

Reserve Capacity refers to the capacity of the battery without engine alternator current. The engine alternator powers the boat appliances in tandem with the marine battery. Therefore, knowing the reserve capacity can be useful to determine the duration the appliances can run when the engine is off.

Marine Battery Voltage

Marine battery voltage should be the same as the voltage rating of the boat appliances. Every boat electrical system comes with a specific voltage rating. The battery you choose should match this voltage rating. Batteries with different voltages are not interchangeable. Using different voltage batteries can fry the electrical equipment in the boat.

There are three voltage ratings for marine batteries:

  • 6V
  • 12V
  • 24V

Among these, the 6v system is very rare and outdated. The 24V system is also rare, generally found on larger boats. 12V batteries are the commonly used standard for marine purposes.

Marine Battery Size

Marine battery size is divided into various standard classes. Each class has a specific size. Therefore, a battery compartment of a particular size will have a dedicated class to it. This provides convenience when replacing batteries.

There are three size groups for marine batteries, Group 24, Group 27, and Group 31. Besides these three, there is also a special group 8D. The groups have multiple subclasses Here is a size chart of each marine battery class:


Size (inches)


10.25 x 6.81 x 8.88


10.75 x 6.81 x 8.88


10.25 x 6.81 x 9.38


10.25 x 6.81 x 9


10.25 x 6.81 x 9.75


12.06 x 6.81 x 8.88


12.5 x 6.81 x 8.94


11.75 x 6.81 x 9.25


13 x 6.72 x 9.44


20.75 x 11.13 x 9.88

Marine Battery Chemistry

There are a lot of options when it comes to marine battery chemistry. Each of these types of marine batteries has its benefits, limitations, and preferred applications. Let us study these applications one by one:

Flooded Batteries

A flooded battery is a primitive type of lead acid battery. These contain heavy lead plates in an electrolyte solution. These batteries face a lot of troubles during operation. Common issues with these batteries are leakage, shorter lifespan, and low depth of discharge.

AGM Batteries

AGM stands for Absorbent Glass Mat. Absorbed Glass Mat is a specific type of lead-acid battery. They contain a glass mat dipped in electrolyte instead of a liquid solution. This eliminates the issue of battery acid spillage.

However, AGM batteries still face many of the shortcomings of lead-acid batteries. For instance, these batteries still have a shorter lifespan and low depth of discharge as compared to lithium batteries.

Gel Batteries

Gel battery is also known as Valve Regulated Lead Acid battery (VRLA). Sometimes, VRLA batteries can also include AGM batteries. Gel batteries contain a silica gel-based electrolyte. This eliminates the risk of spillage and electrolyte top-ups.

However, gel batteries have tedious maintenance requirements. They require venting for the release of build-up gases. In addition, the performance of these batteries is not adequate.

Lithium-ion Batteries

Lithium-ion Batteries

Lithium-ion batteries are the most preferred option for marine batteries. These batteries eliminate the need for electrolyte top-ups or venting. They contain a lithium-based electrode and a graphite electrode. The lithium-based electrode has several options in terms of material. Therefore, many different variations of lithium-ion batteries have emerged.

Lithium Iron Phosphate Batteries

Lithium iron phosphate batteries are the best-performing lithium batteries. They have a Lithium Iron Phosphate (LiFePO4) cathode and a graphite anode. They are often abbreviated as LiFePO4 batteries or LFP batteries.

LFP batteries have a significantly longer lifespan than other batteries. Additionally, they have exceptional depth of discharge. These factors and other reasons, like environmental benefits, make LFP batteries the best option as marine batteries.

How Do You Charge a Marine Battery?

Marine batteries usually derive power from the engine alternator of the boat. There is an onboard charger on the boat for this purpose. However, most manufacturers recommend using the specific battery charger that comes with the battery. Even if the battery doesn’t come with a charger, the manufacturer will always recommend the type of charger that will work well with the battery.

Using third-party chargers not recommended by the manufacturer can damage the battery. These damages are not noticeable at times, but they affect the battery in the long term. For instance, the battery can get overcharged or undercharged, resulting in a permanent loss of battery capacity.

How to Choose a Marine Battery?

How to Choose a Marine Battery?

Choosing a marine battery can be difficult due to the countless options present. However, the choice becomes easy when you focus on the important factors. Here are some of the things to consider:

  • Capacity: First and foremost, the battery capacity should meet the load requirements of your boat. There are always certain electrical losses involved. Therefore, get a battery capacity higher than the load you intend to run. Take careful consideration to including heavy equipment like trolling motors.
  • Battery Type: Many types of marine batteries like AGM, Gel, and Lithium exist. Get a battery type that meets your requirements. For instance, lead-acid batteries can be cheaper but don’t last long. Lithium batteries cost more but provide a better value for money.
  • Size and Weight: The size of the battery is important when replacing an already existing battery. The new battery should fit in the battery compartment you have.
  • Brand: Non-branded batteries are cheaper but can fail frequently. Batteries from a reputed brand like Eco Tree Lithium go the extra mile. Unexpected battery failure is improbable with a reliable battery.
  • Maintenance: Some batteries require more maintenance than other batteries. For instance, flooded batteries require a frequent top-up of battery acid. On the other hand, LFP batteries are designed to require the least maintenance. There is no truly maintenance-free battery.
  • Warranty: A longer period of warranty reflects the brand has more faith in the battery. Longer warranties mean a longer lifespan of the battery. As a matter of fact, Eco Tree Lithium provides a warranty period of 6 years with all of its batteries.
  • CCA: A boat battery can face cold temperatures frequently. Therefore, pay attention to the CCA rating, especially for cranking battery.
  • Deep Cycle Compatible: Many users make the mistake of buying a cranking boat battery instead of a deep cycle one. Check that the new battery can efficiently function in deep cycle batteries usage.
  • Voltage: The voltage rating of the battery and boat should always match. Voltage ratings are not cross-compatible. Therefore, check the voltage rating of the boat electronics before getting the battery.
  • Reserve Capacity: Reserve capacity is important if you want to run boat appliances when the engine is off.
  • Cost: The cost of the battery is an important parameter for most buyers. It is better to consider the cost in terms of value for money instead of initial investment. A battery that costs twice as much might last ten times longer.

Do Marine Batteries Need Maintenance?

Yes, marine batteries need periodic maintenance. The frequency and amount of maintenance can vary depending on the battery chemistry. These batteries operate in highly humid regions. Therefore, corrosion of terminals is a big probability. The battery terminals should frequently be lubricated with petroleum gel or other options. Maintenance steps like these are common for all marine batteries.

Options like lead acid batteries and VRLA batteries require additional maintenance steps. These steps could be electrolyte top-up, release of valve buildup, etc.

How Long Do Marine Batteries Last?

How Long Do Marine Batteries Last

Marine batteries last for six years on average. Lead acid deep cycle batteries can meet the end of life after only about 3-4 years. Lithium batteries, however, can last for over five years. LFP batteries push the limits further and can last more than ten years. An important thing to note is that the battery will fulfil its intended lifespan only with proper maintenance. Reckless use of the battery can result in early battery failure.

How to Store a Marine Battery?

For long-term storage, keeping the marine battery away from the boat is best. The storage place should be warm and dry. Batteries stored in freezing conditions can have irreversible damage. The State of Charge of the battery in storage should be as the manufacturer recommends.

Troubleshooting Common Marine Battery Problems

Troubleshooting Common Marine Battery Problems

Every type of electrical equipment can face issues at some point. With marine batteries, the problems are generally easy to identify and fix. Here are some of the commonly faced marine battery issues:


Corrosion is the most common issue with boat batteries. This is due to the high-humidity environment. It is easy to prevent corrosion by periodically cleaning the battery terminals with a wire brush dipped in a baking soda solution. Corrosion buildup can deteriorate the performance of the battery.

Dead Battery

Marine batteries can become dead if they are discharged beyond their limit. They can also become dead if they are not used regularly. Follow proper charging, discharging, and usage cycles for the battery as the manufacturer recommends.


Sulphation is the buildup of sulphate crystals inside the battery. It is irreversible and reduces the performance of the battery permanently. It will also reduce the battery lifespan. Sulphation is easy to avoid by always keeping the battery above the minimum charge.


Overheating is generally the result of a hot environment. It is also caused by overcharging. Having proper ventilation keeps the battery cool at all times. Disconnecting the charger when the battery is fully charged is also important.


Bulging is a sign of a damaged battery. It occurs due to overcharging or overheating of the battery. It is sometimes followed by leakage of battery fluid. Bulging means that you need to replace the battery. It is easy to avoid by keeping the battery cool and avoiding overcharging.

Internal Short Circuit

Internal short circuits occur when the battery terminals or lead plates come in electrical contact. It may lead to battery failure or even fires. An internal short circuit is easy to avoid with safe battery handling.

Tips to Avoid Marine Battery Problems

Tips to Avoid Marine Battery Problems

Problems in marine batteries usually require a complete battery replacement. However, all the problems are easy to avoid by following the tips mentioned below:

  • Choose the Right Battery: Select the battery that is compatible with the boat. Making any incompatible changes will always lead to trouble.
  • Moisture Free: Moisture is the leading killer of marine batteries. Regularly ensure that the battery terminals are clean and dry.
  • Healthy Charging: Follow the charging habits as prescribed by the manufacturer. Use a genuine charger. Avoid overcharging and overdischarging.
  • Battery Disconnect Switch: Always have a disconnect switch with the battery. Certain components drain battery power even when everything is turned off. The disconnect switch ensures that the battery is not draining without your knowledge.
  • Battery Compartment: A dedicated battery storage box helps prevent the battery from impact and environmental elements. It also prevents battery acid spills from contaminating your boat.
  • Secure Connections: Loose connection points can lead to underperforming batteries. They can also cause sparks and fires. Ensure that the connections are tight and secure.
  • Avoid Battery Overload: All batteries have a recommended discharge energy limit. Using the battery beyond its load limit will reduce its lifespan.
  • Using Battery Monitor: Most boats have a battery monitor that displays the important statistics for the battery. Even so, choose a marine battery that comes with its own battery management system.

Where to Buy a Marine Battery?

Eco Tree Lithium is the lead marketplace for marine batteries. It provides marine battery solutions in many different capacities and features. These batteries have the option of a built-in heater that ensures smooth battery operation even in freezing conditions.

Eco Tree Lithium batteries also come with a battery management system (BMS) with all products. BMS provides automatic monitoring of the battery. The astonishing warranty of 6 years provides the peace of mind that the battery is built tough.

What is the Difference Between a Regular Car Battery and a Marine Battery?

A marine deep cycle battery differs from a regular car battery. Marine deep cycle batteries have thicker plates designed for slower discharges. The deep cycle batteries will provide a low charging current for long periods of time. On the other hand, regular car batteries are designed to provide a high current for a short period of time.

Replacing a marine battery with a car battery is never a good choice. Similarly, you cannot use a marine battery in place of a starting battery. Unless you are using a dual purpose battery, starting batteries and deep cycle batteries should be used separately.

What is the Difference Between a Marine Battery and a Leisure Battery?

The difference between marine battery and leisure battery is that marine batteries are used on boats. On the other hand, leisure batteries are used in caravans and motorhomes. Other than that, both of these batteries have the same build and function. Leisure batteries, like marine batteries, are designed for powering many different appliances without an electricity grid.


Marine batteries are crucial to the boat’s functioning. Choosing the wrong battery can result in your boat stalling miles away from any help. Therefore, spending a little extra time and resources when buying your battery can provide unmatchable long-term comfort.