A Guide to Choosing the Best Marine Battery

Table of Contents

A Guide to Choosing the Best Marine Battery

As more and more technology is applied to ships, more power is required to maintain propulsion. In this article, we’ll discuss the most important things to consider when buying a marine battery.

Types of Marine Batteries

It is important to understand the different types available before considering a battery purchase.

The main categories of marine batteries: starter batteries and deep cycle batteries.

Please do not try to replace each other as the batteries will overheat or not have enough power to power the boat. The goal is to buy a starter battery and a deep cycle battery.

Compare Deep-Cycle vs. Starting Batteries

Different marine and driving styles can place varying demands on your battery. It’s important to first determine whether a conventional starting battery will meet your marine’s needs, or whether a deep-cycle or AGM battery is required. Learn about the difference between deep-cycle and starting batteries.

Starting, Lighting, Ignition (SLI) – Starter Batteries

These batteries deliver a large burst of power for a short time as needed for normal engine starting. The battery is then recharged by the alternator. Unlike a deep-cycle battery, starting batteries are not designed to withstand multiple discharge/recharge cycles, and draining it can significantly shorten its life.

Deep-Cycle Batteries

These batteries are designed to provide a steady amount of current over a long period of time. Deep-cycle batteries can be repeatedly discharged and recharged without causing damage or shortening their life. They are well suited to powering numerous electronics and plug-in accessories, or other applications that place high demands on them such as marine.

Some deep-cycle batteries can be used for engine starting as well (these are sometimes referred to as dual-purpose), but be sure to check the CCA rating to ensure the battery has sufficient starting power.

The deep cycle battery powers other necessary accessories, including:

Trolling motor

Fish finder

DC lamp


Such a device does not require the burst of power required to start a marine motor. Instead, these components need to spread power at a lower rate.

Therefore, deep cycle batteries are charged at the end of each day. To avoid damage from constant charging, they are made of thick lead sheets.

If your boat is too small to accommodate two batteries, only use the boat dual-use option.

Dual-Purpose Batteries

With large, thick plates containing more antimony than starting batteries and an active lead paste chemistry, dual-purpose batteries are a good compromise, tolerating deep discharges that would ruin a typical starting battery. Since they have lower storage capacity than comparably-sized deep cycles, we recommend them for the following applications:

  • Runabouts or other small powerboats using a single battery for both starting and running loads with the engine turned off.
  • Sailboats with two identical batteries used interchangeably for starting and house electrical loads.
  • Boats with one battery bank that does double-duty for house applications and engine starting.

Battery Chemistries

You can choose from among four different battery chemistries: Flooded lead acid, gel, AGM (Absorbed Glass Mat) and Lfp. We suggest you select the battery chemistry based on your needs (deep cycle versus starting versus dual-purpose) and on the performance you desire balanced against your budget.

Flooded lead acid batteries

Flooded lead acid batteries (sometimes called “wet cell” lead acid batteries) are the most common type of deep cycle solar battery. They have been in use for decades, are well understood, and are the least expensive solar storage battery up front (though Lithium ion solar batteries are more cost-effective over time).

Gel Batteries

A gel battery (often referred to as a gel cell battery) is a lead-acid battery that is valve regulated. When the electrolyte is mixed with sulphuric acid and silica, it becomes a relatively stationary gel substance.

What is an AGM Battery?

An AGM battery is a car battery designed for two jobs: delivering powerful bursts of starting amps and running electronics for a long time.

And here’s the big deal: They tend to last longer than a regular flooded battery.

The acronym stands for “absorbed glass mat” and that’s one of many improvements made to Planté’s original train light battery. Glass mats, cushioning the ultra-thin lead plates, will squish like a sponge. In turn, manufacturers can squeeze more glass mats and lead into one battery. More lead equals more power. Plus, that squish factor means the battery’s insides are packed tightly.

AGM batteries also have valves regulating the amount of hydrogen and oxygen gas allowed to escape during charging. They fall under a broader category of valve-regulated, lead-acid (VRLA) batteries, typically used for storing a lot of power for a long time or for long-running power uses.

Developed in the late 1970s, AGM batteries mostly served as backup power for telephone boxes and early computer rooms. Their use expanded over the decades to include motorcycles, military, aircraft, submarines and power banks for offices.

Now, they’re showing up in everyday cars and trucks. Why? What’s the big difference between agms and a standard, flooded battery?

What’s the Difference Between an AGM and a Regular Marine Battery?

AGM car batteries have unbeatable advantages over standard, flooded batteries:

  • More starts per battery
  • Faster recharging
  • More durable construction
  • Safer to handle
  • Special valves protecting the battery’s lifespan

Over the course of their lifespan, AGM batteries can start an engine more than 60,000 times. That’s more than three times the starts you’ll get out of a conventional battery.

And agms recharge faster than typical batteries. Starting your engine depletes your battery only a small amount before the alternator takes over. When it does, the alternator recharges the battery — and keeps all the electrical components running in the car.

Because of their absorbed mats, agms withstand shaking and vibration better than typical batteries. They’re also listed as spill-proof, meaning the regulations are more relaxed about transporting them by air or by road.

How AGM Batteries Work

The superpowers of an AGM battery come from two novel additions to Planté’s invention and a host of small design changes that fundamentally expand what car batteries can do.

First, a valve prevents evaporated water from leaving the battery case. This might not sound like much more than the inverse of the one-way valves on coffee bean bags.

But this little trick is the secret to an AGM’s long life. Here’s how.

Its fundamental chemistry is still based on lead, sulfuric acid and water. When you draw power, the acid molecules move to the lead plates, leaving water and lead sulfate. You are removing the sulfuric acid from the solution to enable a chemical reaction between the paste on the plates. This process is reversed when you charge the battery.

However, there’s always a chance some water loss can happen when electricity splits H2O into hydrogen and oxygen gases. Losing those water molecules means the electrolyte stays more acidic than usual — cutting into the potential strength of the chemical reaction on the plates, and ultimately shortening the life span.

The AGM’s valve stops those gases from leaving.

Except if you’re overcharging the battery. When you use the wrong charger for an AGM, the current must pass through anything it can. That means breaking up more water molecules and building up too much gas inside. That’s when the safety mechanism kicks in, releasing some gas to reduce the pressure built up inside the battery.

Second: fiberglass mesh mats. They are the GM in AGM (absorbed glass-mat) batteries.

Ultra-thin glass fibers soak up all the electrolyte (water and sulfuric acid) into thin pillows cushioning the lead plates. Instead of the free-flowing liquid inside of a regular car battery, the AGM carries its charge in soaked sponges coating the lead plates. The glass mats’ complete coverage makes it easier to summon more power from an AGM battery — and make it easier to recharge.

In power, speed, long life and durability, the AGM battery has standard batteries beat.

So, why are agms in fewer than 9% of the cars on American roads?

What is a Lfp Battery?

Lfp batteries are a type of lithium-ion battery that uses lfp as the cathode material to store lithium ions. LFP batteries typically use graphite as the anode material. The chemical makeup of LFP batteries gives them a high current rating, good thermal stability, and a long lifecycle. 

Most lfp batteries have four battery cells wired in series. The nominal voltage of an LFP battery cell is 3.2 volts. Connecting four LFP battery cells in series results in a 12-volt battery that is an excellent replacement option for many 12-volt lead-acid batteries.

Lfp Vs. Alternative Lithium-Ion Types

Lfp is just one of the many types of lithium-ion batteries. Changing the chemical compound for the cathode creates different kinds of lithium-ion batteries. Some of the most common options are Lithium Cobalt Oxide (LCO), Lithium Manganese Oxide (LMO), Lithium Nickel Cobalt Aluminum Oxide (NCA), Lithium Nickel Manganese Cobalt Oxide (NMC), and Lithium Titanate (LTO).

Each of these battery types has varying strengths and weaknesses that make them a good fit for different applications. Looking at the main properties of these battery types, we can see where lfp batteries stand and for which applications they are best.

Energy Density

LFP batteries have one of the highest specific power ratings amongst other lithium-ion types. In other words, high specific power means that LFP batteries can deliver high amounts of current and power without overheating.

On the other hand, it is important to keep in mind that LFP batteries have one of the lowest specific energy ratings. Low specific energy means that LFP batteries have less energy storage capacity per weight than other lithium-ion options. This is typically not a big deal because increasing the battery bank’s capacity can be done by connecting multiple batteries in parallel. This may not be ideal for an application where extreme energy density in a very light space is required, like battery electric vehicles.

Battery Life Cycles

Lfp batteries have a life span that starts at about 2,000 full discharge cycles and increases depending on the depth of discharge. Cells and the internal battery management system (BMS) used at Dragonfly Energy have been tested to over 5,000 full discharge cycles while retaining 80% of the original battery’s capacity.

LFP is second only to lithium titanate in lifespan. However, LTO batteries have traditionally been the most expensive lithium-ion battery option, making them cost-prohibitive for most applications.

Discharge Rate

Discharge rate is measured in a multiple of the battery’s capacity, meaning a 1C discharge rate for a 100Ah battery is 100A continuous. Commercially available LFP batteries traditionally have a 1C continuous discharge rating but can exceed this for short periods depending on the battery management system.

LFP cells themselves typically can provide a 25C discharge for short periods safely. The ability to exceed 1C allows you to use LFP batteries in high-power applications that may have startup spikes in the current draw.

Operating Temperatures

LFP batteries don’t enter thermal runaway conditions until around 270 degrees Celsius. Compared to the other common lithium-ion battery options, LFP batteries have the second-highest operating temperature limit.

Exceeding the temperature limit on a lithium-ion battery causes damage and can lead to thermal runaway, possibly resulting in a fire. The high operating limit of LFP significantly decreases the chance of a thermal runaway event. Combined with a high-quality BMS to shut down the cells well before these conditions (at around 57 degrees Celsius), LFP offers significant safety advantages.  

Safety Advantages

LFP batteries are one of the stable chemistries of all of the lithium-ion options. This stability makes them one of the safest options for both consumer-facing and industrial applications.

The only other comparably safe option is lithium titanate, which again is typically cost-prohibitive and does not operate at the correct voltage in most situations for a 12V replacement.

Other Things to Consider When Buying Marine Batteries

Battery size

Look at the battery pack. It’s labeled as group 24, 27, 31, etc., referring to the size of the battery. Match the size to your boat size to make sure it fits.

Remember, a smaller number of packs means a smaller and lighter battery. However, a smaller battery usually means you won’t have enough staying power.


How long will your battery last and how many times can you charge it? These are vital questions.

Always check the Reserve Capacity (RC) to determine how long your battery will last on the water. It is a measurement of the time (in minutes) the battery takes to produce 25 amps at 80 degrees Fahrenheit.

Production Date

Finally, look at the production date on the battery. Choose the most recent to add several months of warranty time to your purchase.

Ask about the charger

Always ask about chargers that can be used with batteries. Some types require specific chargers due to the voltage used. Sometimes, the charger’s voltage can be too high, which can damage the battery.

Also, it’s a good idea to have a charger that doesn’t drain the battery when not in use.

New energy battery: deep cycle lithium iron phosphate battery

DEEP CYCLE BATTERIES With BMS(lifepo4 Lithium Battery)

Low Temperature 24V 60AH Deep Cycle LiFePO4 Battery

Low Temperature 48V 50AH Deep Cycle LiFePO4 Battery

Low Temperature 48V 100AH Deep Cycle LiFePO4 Battery

Low Temperature 48V 200AH Deep Cycle LiFePO4 Battery

Low Temperature 12V 200ah Deep Cycle LiFePO4 Battery

100AH 12V Low Temperature Heating Enable

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