Boat Battery Sizes: Choosing The Right Fit For Your Vessel

Choosing the right size battery for your boat is crucial for optimal performance and reliability. Marine batteries are designed to handle the challenges of the marine environment, such as vibrations, shocks, and water exposure. The size of a marine battery is determined by its physical dimensions, weight, and electrical capacity. When selecting a marine battery, it is essential to consider factors such as the type and size of your boat, power requirements, and climate conditions. Understanding your boat's power needs and the different types of batteries available will help you make an informed decision.

Deep Cycle vs Starter Battery

Marine batteries are unique and differ from standard car starter batteries. They are designed to be fully sealed to prevent leaks and be vibration resistant. Marine batteries can also function as both boat starter and house batteries for limited energy use.

There are three main types of marine batteries: deep cycle, starting, and dual-purpose. Starting batteries, also known as cranking batteries, are designed to provide maximum power for a short duration, about 1-3 seconds, to start a boat's engine. They have thinner and more numerous plates, maximising the surface area to generate high amperage bursts of current.

Deep cycle batteries, on the other hand, provide stable and continuous power over a longer period. They are commonly used in marine applications to power electronics such as sonar, GPS, and radios. Deep cycle batteries have fewer, thicker plates, allowing them to provide a consistent power output over extended periods. They can be completely drained and recharged frequently, and their thicker plate construction makes them less susceptible to overheating.

Dual-purpose batteries combine the functions of both starting and deep cycle batteries. They can be used to start the engine and provide consistent power for trolling motors. However, they may not always provide the same level of performance as two separate batteries.

When choosing a marine battery, it is essential to consider the specific needs of your boat. Smaller boats may be able to use a single battery for both starting and power applications, while larger boats or those with high power consumption should opt for two separate batteries to minimise the risk of stranding on the water due to a dead battery. Additionally, it is recommended to use lithium batteries instead of lead-acid batteries, as they offer longer shelf life, constant power, temperature resistance, faster charging, and lightweight construction.

Battery Weight

The weight of a marine battery depends on its type, size, and chemistry. The weight is an important factor to consider when choosing a battery for your boat, as it can impact the boat's overall weight and performance.

Marine batteries are typically classified as starting, deep cycle, or dual-purpose batteries. The weight of these batteries can vary depending on their size and specific use.

For example, a Group 24 battery is a compact and lightweight option for smaller boats, measuring 10.2 inches in length, 6.8 inches in width, and 9.3 inches in height. On the other hand, a Group 31 battery is a popular choice for larger boats with multiple electronics and is slightly longer, measuring 12.8 inches in length, 6.8 inches in width, and 9.3 inches in height.

The weight of a battery within these groups can vary depending on its chemistry. For instance, a lead-acid Group 24 battery typically weighs between 60 and 80 pounds, while a lithium-ion battery of the same size and capacity would weigh approximately half as much, at around 31 pounds.

The weight of a marine battery is an important consideration when it comes to boat performance. Heavier batteries can impact the overall weight limit of the boat, which can affect its speed, handling, and fuel efficiency.

Additionally, the weight of a battery can be indicative of its power and capacity. Larger and heavier batteries tend to have higher capacities and can provide prolonged usage times, making them suitable for larger boats with higher power demands. Conversely, smaller and lighter batteries are better suited for lower energy applications and are often found on smaller vessels.

Battery Maintenance and Lifespan

The weight of a marine battery can also be a factor when it comes to maintenance and lifespan. Heavier batteries, such as lead-acid batteries, may require more frequent maintenance and tend to have shorter lifespans, especially if they are not properly maintained.

Lithium-ion batteries, on the other hand, require minimal maintenance and typically last much longer, with lifespans of up to 10 times that of lead-acid batteries. This extended lifespan, combined with their reduced weight, makes lithium-ion batteries a popular choice for boaters despite their higher upfront cost.

In summary, the weight of a marine battery is an important consideration when choosing the right battery for your boat. It can impact the boat's performance, weight limit, and overall power availability. By selecting a battery with the appropriate weight and chemistry for your boat's size and power requirements, you can ensure optimal performance and a more enjoyable boating experience.

Battery Chemistry

Marine batteries are available in a variety of chemistries, each with its own advantages and drawbacks. Here is a detailed overview of the different types of marine battery chemistries:

Lead-Acid Batteries

Lead-acid batteries are the most traditional and common type of marine batteries. They are typically constructed with lead plates and acid as the primary ingredients. There are two main variants of lead-acid batteries: flooded lead-acid (FLA) and sealed lead-acid (or valve-regulated lead-acid, VRLA). FLA batteries use a blend of distilled water and sulfuric acid and require regular maintenance, including checking electrolyte levels and adding distilled water. On the other hand, sealed lead-acid batteries are maintenance-free.

Lead-acid batteries are large, heavy, and have long charging times. They often weigh around 80 pounds each, which can add significant weight to a boat. Additionally, their storage capacity is relatively low compared to their overall footprint. Despite these drawbacks, lead-acid batteries are initially lower in cost, making them an attractive option for some boaters. However, their short lifespan of 2 to 4 years may outweigh the initial savings.

Absorbent Glass Mat (AGM) Batteries

AGM batteries are an advanced type of lead-acid battery that uses glass mat separators to hold the electrolyte, resulting in a spill-proof design. One of the key advantages of AGM batteries is their longer lifespan compared to flooded lead-acid batteries. They also require minimal maintenance and have a lower internal resistance, enabling faster charging and discharging. AGM batteries are a great choice for boat owners as they can hold a charge for extended periods without losing energy, making them suitable for both starter and deep cycle applications.

Lithium-Ion (LiFePO4) Batteries

Lithium-ion batteries, specifically LiFePO4 batteries, are a newer option for marine use. These batteries offer several benefits over traditional lead-acid batteries. They are lightweight, durable, and have a longer lifespan. Lithium-ion batteries have a high energy density, providing more power in a smaller package. This makes them ideal for applications where weight and space are concerns. Additionally, they provide a consistent voltage output throughout their discharge cycle.

Another advantage of lithium-ion batteries is their charging efficiency. They can be charged much faster than lead-acid batteries, reducing downtime between trips. Lithium-ion batteries are also safe to drain to below 50% without damaging the battery. However, it is important to note that lithium-ion batteries are more expensive than other types of marine batteries.

In summary, the choice of marine battery chemistry depends on various factors such as weight, maintenance requirements, lifespan, and budget. Lead-acid batteries are a traditional and affordable option, but they have several drawbacks, including weight and maintenance. AGM batteries offer enhancements such as spill-proof design and faster charging, while lithium-ion batteries provide the most advanced technology with their lightweight, durable, and efficient performance. Ultimately, the decision should be based on the specific needs and preferences of the boat owner.

Battery Capacity

When selecting a marine battery, it's important to match the battery's capacity to your boat's power requirements. This involves assessing the type and size of your boat, as larger boats typically need larger batteries. You should also consider the electrical equipment and systems on board, such as electronics, lights, pumps, and appliances, and calculate their total power consumption. Additionally, climate conditions can impact battery performance and lifespan, so choosing a battery with the appropriate cold cranking amps (CCA) or reserve capacity (RC) for your boating climate is essential.

The Battery Council International (BCI) has established a set of standard group sizes to help boat owners choose the right battery. The most common marine battery group sizes are 24, 27, 31, and 8D, and they are tailored to specific boat types, from low-consumption vessels to more demanding motorboats. Generally, a larger group size corresponds to a larger battery capacity.

When it comes to battery chemistry, there are two main types of marine batteries: lead-acid and lithium. Lead-acid batteries are traditional, affordable, and require regular maintenance, while lithium batteries are newer, lightweight, durable, and have a longer lifespan. Lithium batteries, such as LiFePO4 batteries, offer incredible energy density and a high cycle life, making them ideal for applications where weight and space are concerns. They also have faster charging capabilities, which reduce downtime between trips.

In summary, selecting the right battery capacity for your boat involves carefully considering your boat's power requirements, choosing the appropriate battery group size, and selecting the best battery chemistry for your needs. By taking these factors into account, you can ensure your boat's electrical system performs reliably and efficiently.

Battery Maintenance

Marine batteries are specifically designed for the heavy draw of long days of use with trolling motors and outboards. They are one of the most vital parts of your boat's electrical system. Therefore, it is crucial to look after them.

• Follow the manufacturer's instructions for proper charging.
• Do not overcharge the battery as it can affect its lifespan.
• Keep the battery clean and free of any dust or debris.
• Regularly inspect the connections and terminals for any corrosion.
• Store the battery in a cool, dry place when not in use to maintain its condition for extended periods.
• Keep the area around the battery ventilated, especially during charging.
• Turn off the battery master switch when you leave the vessel.
• Disconnect the batteries and store them in a cool, dry place if you will not be using your boat for a long period.
• Check the electrolyte or water level in the battery before each charge and keep it filled to the manufacturer's recommendations. Do not overfill.
• Always use marine batteries – cranking or starting type for the outboard and deep cycle for the trolling motor.
• Charge the batteries as soon as possible after a fishing trip. The longer the battery stays discharged, the shorter its life will be.
• Clean the terminals every three months, if you are not using a connector.
• Check all the connections for tightness.
• Use standard batteries as they are designed to withstand challenging water and weather conditions.
• Use one type of battery as recommended by the boat dealer. Using different types can lead to underperformance of your boat electronics and shorten the battery bank's lifespan.
• Keep batteries cool and dry.
• Check terminal connectors regularly to avoid loss of conductivity.
• Add distilled water to flooded lead-acid batteries when needed.
• Keep them charged. Leaving them discharged for any length of time will damage them and lower their capacity.
• Clean corrosion with a paste of baking soda and water.

Frequently asked questions