Choosing the correct marine battery size is a critical decision for boaters. Whether you're a first-time boat owner or a seasoned sailor, understanding the factors involved in selecting the appropriate marine battery size is crucial for optimal performance. This article will provide you with valuable insights and practical tips to help you make an informed decision.

What is A Marine Battery

A marine battery is a specially designed deep-cycle battery that is used to power boats and other watercraft. It is built to handle the challenges of marine environments, such as vibrations, shocks, and constant exposure to water. Marine batteries are typically deep cycle batteries, meaning they can be discharged and recharged repeatedly without losing their capacity. They provide the necessary power for starting the boat's engine, running electrical systems, and powering auxiliary equipment onboard.

what is marine batttery

How Does Marine Battery Size Matter?

Marine battery size matters because it directly affects the performance and reliability of your boat's electrical system. Choosing the right size marine battery ensures that you have enough power to start your engine, run your electronics, and meet your power demands while out on the water.

The size of a marine battery is typically determined by its physical dimensions, weight, and its electrical capacity. A battery's electrical capacity is measured in ampere-hours (Ah) and refers to the total amount of charge it can deliver over a specified time period.

How To Select A Marine Battery Size

When selecting a marine battery size, you need to consider several factors:

  • Boat Type and Size: Different types and sizes of boats have different power requirements. Larger boats, for example, will typically need larger batteries to accommodate their electrical systems and equipment.
  • Power Requirements: Determine the electrical equipment and systems you have onboard that require power. This includes electronics, lights, pumps, appliances, and any additional accessories. Calculate the total power consumption to determine your battery size requirements.
  • Climate Conditions: Extreme temperatures, both hot and cold, can affect the performance and lifespan of a battery. Depending on your boating climate, you may need to choose a battery with appropriate cold cranking amps (CCA) or reserve capacity (RC) to ensure reliable performance in those conditions.

By carefully considering boat type, power requirements, and climate conditions, you can select the correct marine battery size that will meet your specific needs and ensure dependable power on the water.

How to Calculate Your Boat’s Power Needs?

Here are some steps you can refer to calculate the boat’s power need:

  • 1. Create a checklist of all the electrical devices on your boat, including lights, bilge pumps, trolling motors, and other gadgets.
  • 2. Determine the electrical consumption of each device. This value is usually listed in amps in the boat's manufacturer manual. If not available, use a multimeter to measure the amps.
  • 3. Note the running time for each device. This is the duration you intend to use each device during one charge cycle.
  • 4. Calculate the Amp-hour rating of each device by multiplying the amp consumption by the running time. For example, if a light bulb consumes 1 amp and runs for 6 hours a day, the power draw would be 6 amp-hours (Ah).
  • 5. Add up the Amp-hour ratings of all the devices to determine the total power draw for the boat.
  • 6. Consider adding a 20% to 30% margin to account for losses and higher electrical requirements at times.
  • 7. Based on the total electrical consumption, determine the Amp-hour battery rating that will meet your requirements. Purchase a battery with this Ah rating, as batteries in the market are listed by their Amp-hours.

Another way to express the same meaning is by calculating the total wattage of the electrical load. This is useful when you have the watt rating of each device. To find the Amp-hour rating, divide the total wattage by the voltage of the boat system.

For example, let's say you have a 20 W light, a 10 W navigation system, a 40 W autopilot system, a 10 W radar, 40 W navigation lights, and a 30 W watermaker. The total wattage would be:

  • Total wattage = 20 + 10 + 40 + 10 + 40 + 30 = 150 W
  • If you plan to use these devices for six hours on a single charge, the Watt-hour rating would be:
  • Watt-hours = 150 W x 6 hours = 900 Wh
  • To find the Amp-hour rating for a 12V boat system, divide the Watt-hours by the voltage:
  • Ah = 900 Wh ÷ 12V = 75 Ah

Therefore, the battery you need for the boat is at least 12V 75Ah, a 12V 100Ah battery would be suitable.

Types Of Marine Battery Based on The Chemistry

There are several types of marine batteries based on their chemistry. Here are a few common ones:

1. Lead Acid Battery

Lead-acid batteries are the most common and affordable type of marine batteries. They have been in use for a long time and come in two variants: flooded and sealed. Flooded lead-acid batteries require regular maintenance, including checking electrolyte levels and replenishing distilled water. Sealed lead-acid batteries, also known as valve-regulated lead-acid (VRLA) batteries, are maintenance-free.

2. Absorbent Glass Mat (AGM) Batteries

AGM batteries are an advanced type of lead-acid battery. They use glass mat separators to hold the electrolyte, resulting in a spill-proof design. AGM batteries have a longer lifespan compared to flooded lead-acid batteries and require minimal maintenance. They also have a lower internal resistance, allowing for faster charging and discharging.

3. Lithium-Ion (LiFePO4) Batteries

Lithium-ion batteries are the most advanced and expensive option. In marine applications, the type of lithium battery is LiFePO4 battery. They offer incredible energy density and a high cycle life. Li-ion batteries are much lighter and more compact than lead-acid batteries, making them ideal for applications where weight and space are concerns. They also provide a consistent voltage output throughout their discharge cycle.

These are just a few examples of marine battery types based on their chemistry. Each type has its own advantages and considerations, so it's important to assess your specific needs and budget before making a decision.

Why LiFePO4 Batteries are the Most Recommended

LiFePO4 lithium batteries are often considered the best option for marine boats due to several advantages they offer in terms of weight, lifespan, and other important factors. Here's an explanation of these advantages:

  • Weight: LiFePO4 lithium batteries are significantly lighter than traditional lead-acid batteries. This weight reduction can be crucial for marine applications, as it allows for increased fuel efficiency and more accessible placement within the boat. The lighter weight also helps to improve the overall performance of the vessel, especially in terms of speed and maneuverability.
  • Lifespan: LiFePO4 lithium batteries tend to have a longer lifespan compared to other battery types. They can endure a higher number of charge cycles, which means they can be charged and discharged more times before their performance starts to degrade. The high-quality LiFePO4 batteries like Power Queen have the life cycle up to 4000-15000, while lead-acid batteries only have 300-500. This extended lifespan is beneficial for marine applications where reliability and durability are crucial, as it reduces the need for frequent battery replacements.
  • Depth of Discharge: LiFePO4 lithium batteries can be discharged to a greater extent without causing any harm. They can typically be discharged up to 80-90% of their capacity without negatively affecting their overall lifespan or efficiency. This deeper discharge capability provides more usable capacity for marine applications and allows for longer operating times on a single charge.
  • Charging Efficiency: LiFePO4 lithium batteries have excellent charging efficiency, allowing them to charge much faster compared to other battery types, such as lead-acid batteries. This faster charging capability is beneficial for marine boats as it reduces downtime and allows for quicker turnaround times between trips.
  • Size and Space Efficiency: Lithium-ion batteries have a higher energy density, which means they can store more energy in a smaller package compared to other battery chemistries. This compact size allows for greater flexibility in boat design and provides more space for other essential equipment onboard.

lithium trolling motor battery

Although their initial cost is higher than other types of batteries, the ultra-long lifespan and other benefits make it still worthy investment.

Learn more about the reviews about Power Queen.

The Standard Size of Marine Battery

The standard size of marine batteries can vary depending on the specific application and boat size. However, the most common marine battery size is Group 24, which typically has a capacity of around 75-85 amp-hours (Ah). Group 27 and Group 31 batteries are also widely used in marine applications, offering higher capacities of around 90-105 Ah and 95-125 Ah, respectively.

These sizes are commonly available in different battery chemistries like lead-acid, AGM, and lithium-ion. Larger boats may require multiple batteries or larger capacity batteries to meet their power demands. It is essential to consider factors such as the electrical load requirements, expected runtime, and available space before selecting the appropriate battery size for your specific marine application.

marine battery size

Different Types of Trolling Motor

There are a few different types of trolling motors that you can use for your boat. Here are some of the common types:

Transom Mount Trolling Motor

This is the most popular type of trolling motor and is mounted on the back (transom) of the boat. It is easy to install and can be adjusted to different angles. Transom mount motors are versatile, suitable for various boat sizes and types.

Bow Mount Trolling Motor

Bow mount trolling motors are mounted on the front (bow) of the boat. They provide better maneuverability and control, especially in wind and rough water conditions. These motors usually have features like GPS integration and wireless control.

Engine Mount Trolling Motor

Also known as auxiliary motors, engine mount trolling motors are mounted directly onto the cavitation plate of an outboard or inboard engine. They are ideal for larger boats and can be used as a primary drive system or to supplement the main engine.

Hand-Controlled Trolling Motor

These trolling motors have a tiller handle that allows you to control the motor manually. They are generally more affordable, easy to use, and suitable for smaller boats or anglers who prefer a hands-on approach.

Foot-Controlled Trolling Motor

Foot-controlled motors are operated using a pedal system, allowing for hands-free operation. They offer precise control and are popular among anglers who want to focus on fishing without constantly adjusting the motor.

Remote-Controlled Trolling Motor

These trolling motors come with a wireless remote control that allows you to control the motor from anywhere on your boat. Remote-controlled motors provide convenience and flexibility, especially for anglers who want to move around while operating the motor.

The choice of trolling motor type depends on factors such as boat size, fishing style, water conditions, and personal preference. It's important to consider your specific needs and the features that will enhance your boating and fishing experience.

Size Recommend For Trolling Motor

The amp-hour rating of a battery directly affects the amount of runtime it can provide. It is crucial to select a lithium battery with enough continuous discharge amperage to match the maximum amp draw of the trolling motor. If you experience any problems with your trolling motor while using lithium batteries, it is essential to ensure that there is enough continuous amperage available for the motor to operate at its maximum amp draw. The chart below displays the maximum amp draw based on motor thrust.


Note: A starting battery is not suitable for use with an electric trolling motor.

Thrust Range

LiFePO4 Battery Capacity

Recommended Battery

30 to 55 pounds

50-100 Ah

Power Queen 12V 100Ah

Power Queen 12V 100Ah mini

55 to 80 pounds

100-150 Ah

Power Queen 12V 200Ah

80 to 100 pounds

150-200 Ah

Power Queen 12V 300Ah

200 to 300 pounds

200-300 Ah

Power Queen 12V 410Ah


Marine Battery Maintenance and Care Tips

Proper maintenance and care are crucial for ensuring the longevity and performance of your marine battery. Here are some tips to help you keep your battery in good condition:

  • Charging: Follow the manufacturer's instructions for charging your battery. It's generally recommended to use a smart charger designed for marine batteries, which will monitor and adjust the charging process to prevent overcharging.
  • Storage: If you're not using your boat for an extended period, remove the battery and store it in a cool and dry place. Make sure to periodically charge it to maintain its charge level and prevent sulfation.
  • Cleanliness: Keep your battery clean and free from dirt, grime, and corrosion. Regularly inspect the terminals for any signs of buildup and clean them with a wire brush or specific battery cleaning solution if needed.
  • Connections: Ensure that the battery connections are tight and secure. Loose connections can result in poor performance and reduce the battery's lifespan.
  • Electrolyte levels (for lead-acid batteries): If you have a lead-acid battery, check the electrolyte levels regularly. If they are low, add distilled water to bring them up to the recommended level.
  • Avoid deep discharges: Try to prevent deep discharges of your battery, as this can shorten its lifespan. Recharge the battery promptly after use, and don't let it sit for extended periods in a discharged state.
  • Temperature considerations: Extreme temperatures can affect battery performance. Avoid exposing your battery to excessive heat or cold, as it can reduce its capacity and lifespan.
  • Regular inspections: Routinely inspect your battery for any signs of damage or wear. If you notice bulges, cracks, or any other abnormalities, it may be time to replace the battery.

Remember to always refer to the manufacturer's guidelines and recommendations for specific care instructions related to your marine battery.

Frequently Asked Questions (FAQs) about Marine Battery

1. Can you mix battery sizes on the boat?

It is generally not recommended to mix battery sizes on a boat. It is best to have batteries of the same size, type, and age in the same battery bank. Mixing different sizes or capacities can create imbalances in the charging and discharging process, leading to reduced performance and potentially damaging the batteries. It's best to ensure consistency in the battery bank to optimize performance and extend the lifespan of your batteries.

2. What is the most common marine battery size?

The most common marine battery size is typically Group 24. Group 24 batteries are widely used in various marine applications, including as starting batteries for smaller boats and as dual-purpose batteries for boats with moderate electrical demands. These batteries offer a good balance between size, capacity, and affordability, making them a popular choice for many boaters. However, it's important to note that the appropriate battery size depends on individual power requirements, so it's always best to consult manufacturer recommendations for your specific setup.

3.Does a boat need a deep cycle battery?

Deep-cycle marine batteries are specifically designed for continuous discharge and cyclic use, making them an essential component for boaters. Unlike starting batteries, which are optimized for cranking an engine, deep-cycle batteries are built to provide a steady and reliable source of power over an extended period of time. This makes them ideal for running electronics, trolling motors, and other accessories on a boat.