What Size Marine Battery Do I Need in 2024?

Trying to figure out what size marine battery you need for your boating power requirements? We’ll help you understand what to look for and how to select the right size battery for your marine applications.  

Marine batteries are the unsung heroes of any boat battery setup, providing the necessary energy to start engines, power trolling motors and operate countless onboard electrical devices. 

But with so many options available, you might ask yourself, "What size marine battery do I need?"

In this post, we will explore the various types of marine batteries, their sizes, purposes and the factors to consider when selecting the perfect battery for your boat.

You will need to consider both the physical size of the battery you are searching for (the Battery Group Size) as well as the amount of usable power in amp hours. One battery may or may not be the right option for you, depending on your battery bank and whether you have a dual purpose battery that can handle both engine starting and the house loads on the electrical system (such as radio, fish finder, speakers, etc).  

By the end, you will have a deeper understanding of marine batteries and be well-equipped to make an informed decision that will keep your boat powered and ready for adventure.

KEY TAKEAWAYS

• Select the right marine battery for your vessel based on purpose, performance requirements, budget, capacity and cycle life.
• Boat battery options include a starting battery, electrical system or deep cycle battery, dual purpose marine battery and potentially a separate trolling motor battery
• You will need to consider the physical size of the battery (battery group size) AND the battery capacity to find a boat battery with the most usable power. 
• Proper charging techniques and regular maintenance can help extend its lifespan and performance.

What Kind of Marine Batteries Do I Need?

When it comes to marine batteries, one size does not fit all. Different types of marine batteries cater to specific purposes and applications, ensuring optimal performance for your vessel's unique needs. 

So before you can determine what size marine battery you need, you must first determine what type of battery you need and how much power you require. 

The three main types of marine batteries are starting batteries, deep cycle batteries (or auxiliary batteries), and trolling motor batteries. Each of these battery types serves a distinct function: 

• Starting batteries provide a brief surge of cranking amps to initiate the engine, 
• Deep cycle batteries offer a consistent power source for extended periods often used for powering electronic devices such as stereos, speakers and fish finders, and 
• Trolling motor batteries are specifically designed for powering electric motors.

Understanding the differences between these battery types is crucial in selecting the ideal battery for your boat. Additionally, it's important to consider factors such as performance requirements, budget, battery capacity, C-rate, load, usage time and cycle life when making a decision. 

With this information in hand, you can confidently choose the perfect marine battery to power your water adventures.

Marine Starting Batteries

Marine starting batteries closely resemble car batteries, providing a short burst of cranking amps to the engine when the ignition is activated, enabling the engine of the boat to start. These batteries must be able to discharge a large amount of power in a short amount of time as they are only required to kickstart the motor in a matter of a few seconds. 

Some marine batteries are dual-purpose batteries, which can be used for both starting and deep cycle applications. Dual-purpose batteries have enough oomph to start the motor but also retain enough power to keep your onboard electronics powered up as well. 

However, marine starting batteries have their limitations. They generally possess a relatively low battery capacity and depth of discharge (unless using lithium batteries, such as our ProConnect Series Fishing Batteries) and should be discharged at a minimal percentage of their capacity. 

Furthermore, they should not be utilized to power up high-power draw appliances or as use as a trolling motor battery. These batteries are specifically designed for engine start-up and should be used accordingly. It is a good idea to have a separate trolling motor battery for those devices that require a lot of usable power over long periods of time on the water. 

A common starting battery for many boats are flooded lead acid batteries and AGM batteries. However, at Enduro Power Batteries we know the limitations of traditional lead acid batteries and we have designed our ProConnect Series lithium batteries to be the best marine starter battery on the market. 

Our 12V 120Ah lithium LiFePo4 battery is the best lithium starting battery available. As a dual-purpose marine battery, it will provide plenty of cranking amps to start your motor while allowing you to power essential marine electronics for long periods on the water.   

 

SHOP OUR PROCONNECT SERIES LITHIUM BATTERIES FOR MARINE APPLICATIONS

 

Marine Deep Cycle Batteries

Deep cycle batteries are designed to provide power to the electrical loads on your boat when no charging source is available. Unlike lead acid starter batteries, deep-cycle marine batteries can be depleted and recharged multiple times. 

They are typically used to power navigation aids, fish finders, running lights, radios and even trolling motors - though the best trolling motor batteries power trolling motors separately. The lifespan of wet cell deep-cycle batteries generally ranges from a few hundred to over a thousand charging cycles.

Our ProConnect Series dual purpose lithium batteries act both as a starting battery as well as covering the functions of a traditional deep-cycle battery. They are longer lasting than their lead acid counterparts - the AGM batteries and gel batteries - weigh less, have greater battery capacity and can handle bumping around on rough waters.  

When selecting a deep-cycle marine battery, it's essential to consider your boat's power requirements and choose a battery with the appropriate capacity and performance characteristics.

Trolling Motor Batteries

Trolling motor batteries are deep-cycle marine batteries with a rating of at least 110 amp-hour. They are generally Group 27 size or larger and should have a minimum of 100 usable amp hours due to the amount of use that is generally asked of them.

Trolling motor batteries are available in 12, 24, or 36-volt configurations, depending on the desired voltage and capacity for your trolling motor. You can choose to wire several 12V batteries in series to achieve 24V or 36V or you can shop for the perfect 24V or 36V stand alone battery.

Our ProConnect trolling motor batteries are all Group 31 (standard) so they are “drop-in” ready, offer consistent thrust and clean power, are lighter weight and offer more run time than other battery options.  

Read Next: Learn why it is important to choose the best 36-volt trolling motor battery. 

Understanding Marine Battery Sizes (Physical Size)

Choosing the appropriate marine battery size is crucial for ensuring optimal performance and power supply for your boat. Marine batteries are divided into several categories based on their group sizes, which help boat owners select the right option based on their vessel's needs.

The group size is an indicator of the physical size of the battery, such that battery manufacturers design batteries to certain common specs that you can easily compare when shopping. 

We’ll cover the common marine battery group sizes in the section below. But it is also essential to compare the different types of marine batteries, such as lithium, AGM, gel, and lead acid, to determine which type is best suited for your specific application. 

We only sell lithium batteries for all marine deep cycle battery purposes because we know that our lithium iron phosphate batteries are superior to all of the options out there. 

In the following sections, we will delve deeper into marine battery group sizes and compare the various types of marine batteries to help you make the best choice for your vessel.

Battery Group Size Characteristics

Marine batteries are available in battery group sizes of Group 24, Group 27, Group 31 and 8D, each catering to different requirements and boat sizes. 

Group 24 batteries are typically used for smaller boats, such as fishing boats, and have an approximate LxWxH dimensions of 10.25” x 6.81” x 8.8”. 

Group 27 batteries are the most commonly used for marine applications and have an approximate L x W x H dimensions of 12.06” x 6.81” x 8.88”. Thus Group 27 has the same width and height, but are nearly 2 inches longer allowing for more battery capacity.  

Group 31 batteries are the largest size and most common among fishing boats. These batteries tend to boast an impressive capacity that caters to the needs of medium and large boats, as well as any electronic devices installed on board. Their L x W x H dimensions are 13” x 6.72” x 9.44.” As you can see, they are longer, slightly narrower and over a half an inch taller than both Group 24 and Group 27 batteries. 

Group 8D batteries are the largest boat batteries and are useful for larger boats. At 20.75” L x 11.13” W x 9.88” H they are nearly two times the length and width of the other marine battery group size options. 

All of our ProConnect Series batteries are “Drop-in” ready, meaning they fit Group 31 battery tray, so you do not need to modify your existing battery tray at all. Plus each battery will provide five times the usable power, is half the weight and has five times the lifespan than existing batteries.

 

Comparing Lithium, AGM and Lead Acid Batteries

Each type of marine battery technology offers unique advantages and disadvantages. Marine absorbed glass mat (AGM) batteries offer excellent discharge currents, which help maintain high capacity. These batteries also boast a great performance-cost ratio because they are more affordable than a comparable lithium battery. But, like other lead acid deep cycle battery options, AGM batteries cannot be run below 50% of their capacity so you must always be mindful of their state of charge. 

For example, lithium batteries (lithium iron phosphate, or LiFePo4) have excellent capacities, C-rates, and a deep depth of discharge, but come at a higher cost. They are lighter in weight, have higher voltage and have a much longer lifespan than any of the lead acid marine batteries they compete with. 

We only manufacture and sell lithium batteries because we know that they are the best boat batteries for any application.  

Understanding the differences between these battery technologies is crucial in selecting the right marine battery for your boat. By weighing the pros and cons of each type, you can make an informed decision that will ensure reliable power and optimal performance for your vessel.

How to Determine the Right Marine Battery Size for Your Boat

Determining the right marine battery size for your boat requires a thorough evaluation of your vessel's power needs and a consideration of its size and weight. By understanding your boat's power requirements and how they relate to the available marine battery group sizes, you can make an informed decision that will provide reliable power and optimal performance for your vessel.

In the following sections, we will explore how to evaluate your boat's power needs and consider its size and weight when selecting the right marine battery size.

Evaluating Your Boat's Power Needs

To estimate your boat's power requirements, compile a list of all electrical equipment on board and assign a current rating to each item. You can then use the formula watts = amps x volts to compute the power consumption of each device. 

It is also recommended to factor in a single amp for every cubic foot of engine space when determining the appropriate marine battery size for your boat. Generally, boat owners opt for a range of 300-500 Cold Cranking Amps (CCAs) for starting their boats, depending on the engine's size.

When selecting a deep-cycle marine battery, it's essential to consider your boat's power requirements and choose a battery with the appropriate capacity and performance characteristics.

For instance, when determining the size of lead-acid batteries, it is recommended to double the battery rating to meet energy requirements. On the other hand, when selecting a lithium battery, it is suggested to base your choice on the energy requirements of your boat because you can use 100% of a lithium battery capacity but only 50% of that of a lead acid battery.

Considering Your Boat's Size and Weight

The size and weight of your boat directly correlate with the size of the marine battery needed to power it. Larger boats require larger batteries to provide adequate power for operation.

To determine the appropriate marine battery size for your boat, it's important to take into account the size and weight of the boat, the type of battery you require, and the power requirements of the boat. 

By considering these factors, you can select the right marine battery size that will ensure reliable power and optimal performance for your vessel.

How long do marine batteries last?

The lifespan of marine batteries can vary greatly depending on factors such as the type of battery, usage frequency, and maintenance. Generally, marine batteries can last anywhere from two to ten years, with lithium batteries providing reliable service for up to 10 years or more.

To maximize the longevity of your marine battery, it is crucial to implement appropriate charging practices and routinely conduct maintenance and inspections.

We back all of our maintenance free lithium boat batteries with a 10 year warranty!

Tips for Extending Marine Battery Life and Performance

Proper care and maintenance can significantly extend the life and performance of your marine battery. In this section, we will provide tips and guidelines for maintaining your marine battery to ensure optimal performance and longevity.

This includes proper charging techniques and regular maintenance and inspection.

Proper Charging Techniques

One of the most important factors in extending marine battery life is using the appropriate charger type and following proper charging techniques. To prevent overcharging, use the charger type specified by the manufacturer and follow the provided instructions. It is also recommended that marine batteries be fully charged between uses to maintain optimal performance.

In addition to using the correct charger, it's essential to store the battery and charger away from extreme heat or cold to prevent damage and ensure optimal charging performance. By adhering to these proper charging techniques, you can greatly extend the life and performance of your marine battery.

Regular Maintenance and Inspection

Routine maintenance and inspection are crucial to prolonging the lifespan of your marine battery. To ensure optimal performance, it is recommended to charge the battery using a marine battery charger, inspect it every few months if not used for extended periods, and recharge it prior to each use.

When inspecting your marine battery, be sure to check the battery terminals at least once a month and verify that they are free from corrosion or dirt. For wet cell batteries, ensure that the electrolyte levels are accurate and replenished as needed.

To avoid the requirement to have to check a flooded lead acid battery regularly, we recommend upgrading to a maintenance free lithium battery. Regardless of what marine battery group size you select, our batteries will not leave you with corroded battery terminals or having to deal with dangerous battery acid. 

By regularly maintaining and inspecting your marine battery, you can ensure its extended lifespan and continued reliable performance.

Summary

Choosing the right marine battery for your boat is essential for ensuring optimal performance and reliable power. By understanding the various types of marine batteries, their sizes, and applications, you can make an informed decision that best suits your boat's needs. 

Additionally, proper care and maintenance, including appropriate charging techniques and regular inspections, can prolong the life and performance of your marine battery. 

With the knowledge gained from this guide, you are now well-equipped to select the perfect marine battery for your vessel and embark on your next aquatic adventure with confidence.