Marine Batteries Buying Guide – All 20 Considerations to Make

How to choose the best marine batteries? It’s a common question among boat owners. Boat or marine batteries perform many vital functions, such as running the equipment onboard. Since boats can be out on the sea for days, weeks, and even months, you must be careful when choosing a marine battery – you’re going to depend on it!

A trend has emerged lately where lithium marine batteries far outperform other alternatives. However, high-capacity marine batteries can be a significant investment. So, invest in the most reliable, efficient, and cost-effective model for your boat.

This article will explore how to choose marine batteries, the factors to consider, and which battery technology performs best in each case.

Why Is It Important to Choose the Right Marine Battery?

Why is It Important to Choose the Right Marine Battery?

Of course, every boat owner wants a battery that can supply the power they need and last for years. A marine battery, specifically designed to handle the harsh conditions of marine environments, is an excellent choice for such needs. These are built robustly to resist water, salt, and shock damage, and are more than just a power source for the boat – they are essential for the safety and convenience of the people onboard too.

For example, galley appliances like a stove or refrigerator depend on the power provided by marine batteries. The electronics we often take for granted in the marine world, such as GPS, trolling motors, windlass, depth finders, and fish locators, also require marine batteries to function. These batteries, given their ability to deliver a steady supply of power, are a lifeline to these devices. An underperforming or malfunctioning battery could mean a boat owner is left stranded in the middle of the ocean without any of the onboard appliances working – a very undesirable situation!

You can avoid such problems by making a wise decision and investing in the best marine battery available, instead of settling for the first one you come across. It’s an investment that ensures not only the functionality of your boat but also your peace of mind while at sea.

What are the Factors to Consider When Choosing a Marine Battery?

Marine batteries are a niche application that has specific requirements. Here are some of the factors you should consider when looking for the best option:

Intended Application

There are various types of marine batteries – not interchangeable – as each is designed for a specific purpose. The main applications are:

Cranking batteries

Cranking refers to starting the marine vehicle. The battery design supplies a large amount of energy in a short amount of time. In addition, it has thin plates so it can be charged easily by the boat’s alternator. Do not use a starter battery to run the appliances onboard your boat. Doing so will damage it and the appliances onboard.

Deep Cycle batteries

A deep-cycle battery supplies a lower amount of energy but for long periods. It can power all the items on the boat. A deep-cycle battery has a significantly longer cycle life than a cranking battery and is designed to supply power for longer. Its thick plates also mean that it charges more slowly.

Dual Purpose Batteries

These are also called hybrid batteries and fulfil the role of starting and deep cycle batteries. However, they typically have a limited capacity, which makes them suitable for only small boats. Choosing a dedicated battery for each purpose, cranking or deep cycle, is always the best option for performance, capacity, and lifespan.

Battery Dimensions

The battery compartment in each marine vehicle is a specific size. So, it is vital to get a battery that fits your boat. For convenience, battery sizes are organised into preassigned groups to make replacement easier. The Battery Council International (BCI) defines the groups and works with carefully selected companies to ensure consumer awareness.

It’s easy to identify the most suitable group by noting down the length (L), breadth (B), and height (H) of your battery.

Here are the different groups with the LxBxH dimensions (inches):

  • 22NF: 9-7/16” x 5-1/2” x 8-15/16”
  • 24M: 10-1/4” x 6-13/16” x 9-3/4”
  • 25: 9-1/16” x 6-7/8” x 8-7/8”
  • 27M: 12-1/2” x 6-13/16” x 9-3/4”
  • 31M: 13” x 6-13/16” x 9-7/16”
  • 34M: 10-1/4” x 6-13/16” x 9-7/16”
  • 35: 9-1/16” x 6-7/8” x 8-7/8”
  • 65: 12-1/6” x 7-9/16” x 7-9/16”

For more information, check our guide on what size marine battery you need for your boat.


Unlike stationary applications such as home solar panels, boats have strict weight limits. Boaters always opt for lighter equipment, and marine batteries are no exception. Check the weight limit for your boat and decide how much of that you can spare for the batteries. Fortunately, lithium batteries weigh around 30% to 50% less than conventional lead-acid versions.

Power Requirement

Power Requirement

Calculating the electric power required by your boat will help you choose the most suitable marine battery. The power is measured in Ampere Hours (Ah) – the number of hours it can supply a constant 1A current.

To calculate the Ampere Hours required to run your boat, determine the current (Amps) each item on your boat draws when connected to the battery. Include even small items such as light bulbs as well. You can measure the current using a multimeter or a system monitor (if your boat has one).

You can also calculate it using the formula:

Current (A) = Power (W) ÷ Voltage (V)

For example, a 12 V system powering a 12 W bulb will draw a current of 1 A (12 W ÷ 12 V). Once you know the current draw, multiply it by how many hours the equipment will be used in a day. If the bulb is used for 8 hours, its Ampere-Hour rating is 8 Ah.

Once you have the Ampere hour value for each piece of equipment, add them to get the overall Ampere-hour value.


Boats are constantly in motion due to the movement of waves in the sea or ocean. So, the battery must be built to withstand the vibrations. Additionally, marine batteries are rarely in constant use. They are typically stored for a long time, followed by intense usage for a short time. Prioritise the quality over saving money.


The lifespan of a battery is a crucial factor to consider, especially if you are planning to enjoy your boat in the long run. When comparing the lifespan, check the warranty the company offers. The warranty often indicates the minimum lifespan of a battery in any working condition.

If a battery manufacturer claims a lifespan of 10 years but provides a 2-year warranty, it’s unlikely the battery will last for 10 years. In this regard, Eco Tree Lithium is way ahead of the competition as its batteries have a long life and come with a 6-year warranty.

Corrosion Resistance

The ability of a marine battery to resist corrosion is vital due to the saltwater conditions in which it operates. Corroded batteries should be disposed of since corrosion can cause fires, explosions, and other hazards. It’s a good idea to keep the terminals lubricated with petroleum jelly since it is the best shield against corrosion.

Maintenance Requirements

Different types of batteries vary in how much maintenance they need. For example, lead acid batteries need frequent attention, which is why most boat owners avoid them. In contrast, lithium batteries require almost no attention.

Charging in Freezing Conditions

If there is a possibility that the boat will operate in regions that have sub-zero temperatures, you must ensure that the battery will work in freezing conditions. Despite the many advantages of lithium batteries, they have a serious shortcoming – they don’t work well in sub-zero temperatures.

In contrast, Eco Tree Lithium LiFePO4 batteries come with a built-in BMS. The BMS, or Battery Management System, heats the battery in case the temperature gets too low, which helps in ensuring the battery can operate perfectly at any temperature.

Battery Chemistry

There are two main classes of batteries: lead-acid and lithium batteries. There is an enormous difference in their respective battery chemistries. There are also many subtypes of each class. Here are some of the common marine battery types:

Flooded Lead Acid (FLA) Batteries

FLA marine batteries, or wet cell batteries, contain two electrode plates separated by a liquid acid electrolyte solution. These are the least preferred option among most boat owners. They have the lowest cycle life of all current battery technologies.

Gel Batteries

Gel Batteries

Gel batteries are one step better than flooded lead acid batteries since they replace the liquid electrolyte with an electrolytic gel. The benefit of gel is that it doesn’t spill as easily as the liquid electrolyte solution. However, the other disadvantages of flooded lead acid batteries remain.

Absorbent Glass Mat (AGM) Batteries

Absorbent glass mat batteries have a glass fibre mat that absorbs the electrolytic solution. These are the most spill-proof lead acid battery option. Their lifespan is better than a flooded or gel-lead acid battery. However, it is still considerably lower than the typical usable life of lithium batteries.

Lead Crystal Batteries

Lead crystal batteries are innovative lead-based batteries designed for faster charging. Their life cycle is also higher than a conventional lead acid battery. These batteries have better safety standards than traditional flooded lead acid batteries and a better operating range.

Lithium Batteries

Lithium Batteries

Lithium Batteries

Modern lithium battery technology has successfully eliminated all of the shortcomings of lead-acid batteries. These batteries don’t have spillable electrolytes, which makes them better than lead acid batteries by leaps and bounds. In lithium batteries, one electrode is a lithium-based compound, and the other is graphite.

There are several lithium compound options available for these batteries. This results in many different lithium battery options. Among all these different types, Lithium Iron Phosphate (LiFePO4 or LFP) batteries have become the most sought-after lithium batteries.

LFP Batteries

A LFP (LiFePO4) battery contains electrodes made out of Lithium Iron Phosphate and Graphite. These batteries are the most stable option among all lithium marine batteries since they do not contain toxic materials like cobalt.

Many lithium batteries have excellent depth of discharge (DoD), up to 80%. LFP batteries take it a step further with 98% to 100% depth of discharge, so you can discharge these batteries to 0% without harming them.

And these batteries provide six to ten times longer lifespans than lead acid batteries, with almost double the capacity.

Which Is the Best Type of Battery for Marine Applications?

Considering all the critical factors when choosing a marine battery, LFP batteries are the best option. Lithium marine batteries offer superior performance to lead acid batteries.

Among lithium batteries, LFP batteries provide the most value for money by offering better safety, longer lifespan, and other benefits such as greater charging capacity and lower weight.

Is Upgrading Your Marine Battery to Lithium Worth It?

If your electric boat has a lead-acid battery, it is worth upgrading to a lithium marine battery. Lithium marine batteries are more dependable and ideal for deep-cycle applications, unlike lead-acid batteries. You can still use a lead acid battery as a cranking battery for the boat.

What Are the Benefits of LiFePO4 Batteries for Marine Applications?

What are the Benefits of LiFePO4 Batteries for Marine Applications?

There are several unique advantages that LiFePO4 batteries bring to the table over other alternatives.

Small and Lightweight

The high energy density of lithium batteries makes it possible to provide a high-capacity battery in a smaller size. It also decreases the weight of the battery, making it ideal for marine applications.

High Cycle Life

LiFePO4 batteries provide upward of 3000 charge/discharge cycles. AGM and alternative lithium marine batteries can only provide a cycle life of 1500 to 2500 charge/discharge cycles.

Longer Lifespan

The high charge and discharge cycles directly translate to a longer lifespan. LFP marine batteries for boats can easily last between ten to fifteen years. Proper care can make them last even longer.

Depth of Discharge (DoD)

Most batteries have a lower discharge limit, after which further discharging will negatively affect the battery life. But the discharge limit for an LFP battery is 0%, without harming it.

High Safety Levels

LFP batteries do not emit toxic gases when operating in a boat. So, there is no need to provide venting or any special requirements. In addition, LFP batteries pose no fire or explosion risk.

Negligible Maintenance

Companies that manufacture batteries often claim their battery as maintenance-free. In reality, no battery doesn’t require some care to maintain it in optimal condition. But LFP batteries require the least attention to maintain them operating for many years.

Operation in Freezing Conditions

Many lithium batteries come with a Battery Management System (BMS) that heats the battery if the working temperature decreases too much. This makes them suitable for use even in freezing conditions.

Is It Easy to Switch to Lithium Marine Batteries?

Yes, switching to lithium marine batteries is easy. The only thing to figure out is the power capacity of the boat and the battery size. Another factor to remember is that to get all the advantages of lithium marine batteries, buy from a reputable supplier such as Eco Tree Lithium.

How Expensive are Lithium Marine Batteries?

Because of their many benefits, people often imagine that LFP batteries are more expensive than they actually are. The cost varies based on the battery capacity you need. Check Eco Tree Lithium’s marine batteries catalogue for more details about the price and features of specific battery products.


Spending time researching before buying marine batteries can eliminate countless potential troubles down the road. Many people make the rookie mistake of going with a lead acid battery instead of a lithium-ion battery, only to have to replace it a year or so later – a waste of money, time and energy.

A lithium marine battery is always the best choice and will handle anything you throw at it (provided it is within its power capacity). A lithium battery often ends up lasting twice as long as the manufacturer claimed if you do not treat it harshly.

Frequently Asked Questions (FAQs)

Here are the answers to some common questions about marine batteries:

1. How many cranking amps should a marine battery have?

The cranking amps of a marine battery usually fall in the range of 100 to 400 Amps. The value mainly depends on the engine that the boat uses.

2. Are lithium batteries safe for boats?

Yes, a lithium battery is a safe option for boats, and LFP batteries are the safest type of battery on the market today.