Everything You Should Know About the Marine Battery

Sailing on a boat can be one of the best feelings in the world, but to properly enjoy it, you should have the confidence that you have a high-capacity marine battery in its best shape. To ensure this, you should know to pick one of the best models available to install on your boat.

To help you choose the right battery for your boat, we are going to cover the basics and even get into some technical details that will help you pick the best option for you. Here you will learn about marine battery applications, how to charge it to extend its lifetime, and much more. We even have a marine battery reviews section with the best available models and a buying guide to help you determine what is the best marine battery for you.

What Are the Different Types of Marine Batteries?

Marine batteries are especially designed to be used on boats. These batteries provide high currents – in many cases, a steady power source for electric motors – and several cranking amps. These batteries are manufactured with heavier plates and casings resistant to pounding and vibrations which are typical on boats.

There are multiple available marine boat batteries types. Here, we will review all of them.

Marine Starting Batteries

A marine starting battery or marine cranking battery is similar to a car battery and the most commonly used option for boats with alternator engines. This battery provides a short burst of cranking amps to the engine when the ignition is activated, allowing it to start the engine of the boat.

The marine cranking battery is designed to have a wider surface by including thinner plates, making it suitable to provide high currents. These batteries tend to have a relatively low capacity, but this is all that they need to properly start the engine of the boat. When the engine alternator kicks in, the boat battery is charged back up to its full capacity.

While the design makes them excellent in providing cranking amps, it limits their capacity and depth of discharge. Starter marine batteries should only be discharged at a small percentage of their capacity and never be used to power up appliances or as a trolling motor battery.

Marine Deep-Cycle Batteries

The deep-cycle or deep-cell marine battery is used to provide a steady power source for angling boats, kayaks, and other boats using trolling motors or other electric motors. This battery is similar to the RV battery and the golf cart battery, since it can be deeply discharged and has a high capacity.

The deep-cycle marine battery is designed with fewer but thicker plates, making it suitable to be discharged at a steady rate for longer periods at a higher depth of discharge. The thicker plates also allow these batteries to withstand high temperatures while providing high electrical currents. The deep-cell marine battery can be drained and recharged many times, while the starter batteries cannot. This is the reason why they are used to power electric motors as well as other devices.

Marine Dual-Purpose Batteries

The dual-purpose marine battery is the midpoint between deep-cell and starter battery and a similar model to the motorcycle battery. Dual-purpose batteries have an internal design that allows them to be deeply discharged and used as starter batteries at the same time.

When looking to save some money and space, you might consider replacing the deep-cycle and starter battery for a dual-purpose marine battery, since it can power the engine and appliances at the same time. This is only recommended for medium and small boats with short trips, since it cannot provide the same depth of discharge as a deep cycle battery nor the cranking amps that a starter battery does.

Marine Battery Group Sizes

Many boats these days have lighting systems, speakers, fish finders, and many other devices installed. While some batteries might not have enough power to handle them, some others can easily power all the devices at the same time. The marine battery group sizes divide all batteries into several categories, making it easier to pick the right option.

Here, you will learn what these marine boat battery group sizes are, what the difference between them is, how to read the marine battery size chart, and what group size battery you should pick your marine battery from concerning the needs of your boat.

What Are the Marine Battery Group Sizes?

The battery group size is a category used to divide the batteries to define their range of capacity, C-rate, and cranking amps in general. These categories were created by the Battery Council International (BCI) to help boat picking the right battery to suit their needs.

In the case of Gel and AGM deep-cycle marine batteries, the rule usually goes like this: the bigger the battery, the higher the capacity. This same criterion is not applicable for starter or dual-purpose batteries, which is why the marine group sizes are a really important criterion to choose a battery.

Marine Battery Size Chart

The marine battery size chart determines a battery category for each marine battery about its size. You might find batteries with slightly bigger or smaller dimensions, but each model should easily fit within a group size when determining its category.

Group SizeLengthWidthHeightEstimated capacity (Ah)Estimated CCA
22NF9.43’’5.5’’8.94’’40-56300-550
24M10.25’’6.81’’9.75’’75-85500-840
259.06’’6.88’’8.88’’
27M12.5’’6.81’’9.75’’66-110640-870
31M13’’6.81’’9.44’’75-125600-1150
34M10.25’’6.81’’9.44’’50-75750-880
359.06’’6.88’’8.88’’
6512.06’’7.56’’7.56’’

Battery size chart

These are some of the most commonly used batteries for all types of boats. The “M” in the marine battery group size chart states that the battery is specially designed for marine applications.

Should You Consider Marine Battery Group Size When Buying a New Battery?

The marine battery group size makes it much easier for boat owners to choose their battery. In some cases, the boats already come with some predefined type of battery that can be installed, and these fall under some of the most common categories on the list.

Group 24 marine battery and group 27 marine battery options are among the most commonly picked and popular choices within the marine battery group size chart. The group 24 marine battery models tend to have a medium capacity, suitable for several marine applications with low- to mid-consumption boats. The group 27 marine battery options have a higher price but also a much higher capacity, making them excellent in powering the motor and several common devices.

Another excellent choice for marine applications is the 31M and 34M group marine batteries. These have relatively high capacities with an excellent C-rate, meaning that they can easily power medium and large boats alongside several electronic devices installed.

Review Section

To pick the best marine battery for your boat, it is important to check out the best available options. In our marine battery review section, we compiled some excellent low-, mid-, and high-end choices. The best thing is that these battery models have a really good performance–cost relation, so you can choose batteries that will cover all your needs within a decent budget.

1. Odyssey 31M-PC2150ST Marine Dual-Purpose Battery – Best Dual-Purpose Marine Battery

Type: Dual purpose | Size: 16.8 x 11.1 x 11.9 in | Weight: 77.8 lbs. | Group size: 31M | Operating voltage: 12V | Technology: SLA AGM | Capacity: 103 Ah | Operating amperage: 103 Ah at C20/2150 PHCA/1150 CCA | Maximum depth of discharge: 80% | Warranty: 4 years
Odyssey 31M-PC2150ST-M Trolling Thunder Marine Dual Purpose Battery
  • Cold Crank Amp (CCA)- 1150 Better warranty: Limited 3 and 4 year full replacement warranty: not pro rata; Longer service life: 3-10 years of service life: save consumers time, money and aggravation
  • Longer cycle life: 70 percentage longer cycle life compared to conventional deep cycle batteries, up to 400 cycles at 80 percentage depth of discharge- high stable voltage for longer periods of time
  • Recharge: Highest recharge efficiency of any sealed lead battery on the market, capable of 100 percentage recharge in 4-6 hours; Mounting flexibility: Non-spillable design

The Odyssey 31M-PC2150ST is one of the best dual-purpose marine battery options available. This is a dual-purpose battery with a great capacity, C-rate, and one of the best warranties you can get for marine application batteries.

This battery has a 103 Ah capacity at C20, meaning that to get its full capacity, you can discharge it at 5.15 amps for 20 hours. As a starter battery, the Odyssey 31M-PC2150ST provides 1150 cranking amps at 0ºF for 30 seconds (1150 CCA) or a 5-second pulse of 2,150 cranking amps at 80ºF (2150 PHCA).

Pros
  • Especially designed casing for marine applications
  • Superior CCA and PHCA compared to other batteries
  • Ideal for all types of boats
  • Superior warranty of 4 years
Cons
  • Higher price compared to other batteries on the list

2. VMAX XTR31-135 Trolling Motor Battery AGM Marine Deep Cycle Group 31 12V 135Ah – Best Deep-Cycle Marine Battery

Type: Deep cycle | Size: 13 x 6.8 x 8.4 in | Weight: 77 lbs. | Group size: 31M | Operating voltage: 12V | Technology: SLA AGM | Capacity: 135 Ah | Operating amperage: 135 at C20/265 min at 25 A/75 min at 75A | Maximum depth of discharge: 80% | Warranty: 1 year
VMAX XTR31-135 Trolling Motor Battery AGM Marine Deep Cycle Group 31 12V 135Ah
  • 12 Volt 135Ah AGM Battery; Dimensions: 13"Lx 6.8"Wx8.7"H; Includes 8mm terminal posts; Reserve Capacity of 265 minutes
  • Maintenance Free Operation: There is no need to check specific gravity of the electrolyte or add water to VMAXTANKS. Can be mounted in any position
  • Rechargeable Sealed battery resists shocks and vibration. High performance AGM technology for long lasting reliable power

Among the best deep-cycle marine battery models, we also find the VMAX XTR31-135. This deep-cycle marine battery has one of the biggest capacities and an excellent C-rate to provide you all the simultaneous amps you might need.

The battery has a capacity of 135 Ah at C20, meaning you can get up to 6.75 amps for 20 hours to enjoy its full capacity. The battery can be discharged faster, at a 75 amp rate for 75 minutes or a 25 amp rate for 265 minutes, but by doing this, you will not get to enjoy its full capacity.

Pros
  • It provides an excellent maximum current of 75 amps.
  • Biggest capacity on the list for an AGM marine battery.
  • Resistant to shocks and vibrations.
  • You can fully use 108 Ah without compromising the battery.
Cons
  • Only 1-year warranty.
  • One of the bulkiest and heaviest models.

3. VMAX MR127 12 Volt 100Ah AGM Deep Cycle Maintenance-Free Battery – Best Battery for Outboard Motor

Type: Deep cycle | Size: 12.1 x 6.7 x 8.2 in | Weight: 68 lbs. | Group size: 27M | Operating voltage: 12V | Technology: SLA AGM | Capacity: 100 Ah | Operating amperage: 100 Ah at C20 | Maximum depth of discharge: 80% | Warranty: 1 year
VMAX MR127 12 Volt 100Ah AGM Deep Cycle Maintenance Free Battery Compatible with Boats and 40-100lb, minnkota, Cobra, sevylor and Other trolling Motor (Group 27 Marine Deep Cycle AGM Battery)
  • 12 Volt 100Ah Group 27 Deep Cycle Heavy Duty AGM Marine Deep Cycle Maintenence Free Battery (Includes carrying handles)
  • Electrolyte Suspension system VMAX tanks utilize an electrolyte suspension system consisting AGM (Absorbed Glass Matt) of a high porosity that totally absorb and contain the electrolyte. No silica...
  • Heavy Duty Grids: VMAX heavy duty lead tin alloys provide an extra margin of performance and service life in either float or cyclic applications, even after repeated over discharges.

The VMAX MR127 is the smallest battery option within the category of 100 Ah or superior capacity AGM marine battery models. This 27M 12V deep-cycle marine battery has an excellent capacity ideal for most boats, great overall performance, and a quality small-sized casing, making it the best battery for outboard motor boats.

This outboard motor battery has a capacity of 100Ah at C20, meaning you get up to 5 amps for 20 hours. You can also get 800 marine cranking amps at 32ºF (800 MCA) or up to 1580 PHCA to start the motor of your boat.

Pros
  • Excellent capacity compared to its size.
  • Great cranking amps for marine applications.
  • Steady current ideal for powering extra devices.
  • The quality casing is specially designed for marine applications.
Cons
  • Only 1-year warranty.

4. Optima 34M BlueTop Marine Starting Battery – Quality Optima Marine Battery

Type: Dual purpose | Size: 10 x 6.88 x 7.8 in | Weight: 38.4 lbs | Group size: 34M | Operating voltage: 12V | Technology: SLA AGM | Capacity: 50 Ah | Operating amperage: 50 Ah at C20/800 CCA/100 minutes at 25 A | Maximum depth of discharge: 80% | Warranty: 2 years
Optima Batteries 8006-006 34M BlueTop Marine Starting Battery
  • 12-Volt, 800 Cold Cranking Amps, Size: 10" x 6 7/8" x 7 13/16" tall, Weight: 38.4 pounds, Dual SAE & 5/16" Stainless Steel Stud Posts
  • Reserve capacity of 100 minutes for constant performance
  • Optimal starting power even in bad weather

Optima is one of the best AGM marine battery manufacturers. The Optima 34M BlueTop is an excellent dual-purpose battery that works both as a deep cycle and starter battery at the same time.

This battery has a 50 Ah capacity at C20, so it provides a steady current of 2.5 amps for 20 hours when deep cycling. You can also power a 25-amp load but only for 100 minutes. The battery provides up to 800 CCA when starting engines, making it an excellent option for small, medium, and some large boats.

Pros
  • Quality casing designed to withstand all types of marine applications.
  • Half the weight of other quality 12V deep cycle marine battery models on the list.
  • Great C-rate.
  • 2-year warranty.
Cons
  • Relatively medium- to low capacity for deep-cycling applications.

5. Mighty Max Battery 12V 55Ah Trolling Battery – Lightest AGM Deep-Cycle Marine Battery

Type: Deep cycle | Size: 9.02 in x 5.43 in x 9.13 in | Weight: 38.58 lbs. | Group size: 22NF | Operating voltage: 12V | Technology: SLA AGM | Capacity: 58 Ah | Operating amperage: 58 Ah at C20/35.2 Ah at C1 | Maximum depth of discharge: 80% | Warranty: 1 year
Sale
12V 55Ah Power Boat Pontoon Electric Trolling Motor Deep Cycle Battery - Mighty Max Battery brand product
  • ML55-12 SLA is a 12V 55AH Sealed Lead Acid (SLA) rechargeable maintenance free battery
  • Dimensions: 9.02 inches x 5.43 inches x 9.13 inches. Listing is for the Battery and Screws only. No wire harness or mounting accessories included
  • SLA / AGM spill proof battery has a characteristic of high discharge rate, wide operating temperatures, long service life and deep discharge recover.

The Mighty Max is one of the lightest and best deep-cycle marine battery models available. With this battery, you can easily power all types of devices on your boat for a fraction of the price.

This AGM deep-cycle battery has a capacity of 58 Ah at C20, meaning you can get 2.9 steady amps for 20 hours. You can also power a 35.2-amp load, but the capacity will drain within 60 minutes. If you require a 24-volt marine battery, you can just plug two of these batteries in series, and they will work flawlessly.

Pros
  • Extremely lightweight when compared to other AGM batteries.
  • A great max current of 35.2 amps.
  • Excellent capacity for such a lightweight option.
Cons
  • The casing is not specially designed for marine applications.
  • Only 1-year warranty.

6. Renogy Deep Cycle AGM Battery 12 Volt 100Ah for RV, Solar Marine, and Off-Grid Applications – Cheapest AGM 12V Deep-Cycle Marine Battery

Type: Deep cycle | Size: 13.1 x 6.9 x 8.6 in | Weight: 63.9 lbs. | Group size: 31M | Operating voltage: 12V | Technology: SLA AGM | Capacity: 100 Ah | Operating amperage: 103 Ah at C10 | Maximum depth of discharge: 80% | Warranty: 2 years
Sale
Renogy Deep Cycle AGM Battery 12 Volt 100Ah for RV, Solar Marine and Off-grid Applications, Gray
  • Maintenance Free: Manufactured with thick absorbent glass mat (AGM) separators and advanced valve regulated technology, Renogy Deep Cycle AGM Batteries save you from acid leakage and frequent...
  • Excellent Discharge Performance: Proprietary quinary alloy plates and specially treated plate grids enable low internal resistance and high discharge currents of up to 10 times the battery rated...
  • Long Shelf Life: Made of high purity materials, Renogy Deep Cycle AGM Batteries reduce the monthly self-discharge rate below 3% at 77℉ (25℃), which is 5 times lower than their flooded counterparts

If you are looking for a high-capacity, deep-cycle battery at a really good price, the Renogy 100Ah is one of the best AGM marine battery options for you. This battery gives you superior capacity and operating amperage that other batteries provide for only a fraction of the price.

The Renogy battery has a 103 Ah capacity at C10, so you can get up to 10.3 amps for 10 hours. The battery can use a max discharge current of 1,100 amps for 5 seconds, but this regular practice will reduce its lifespan. Considering its steady amperage, you can use it as a trolling motor or outboard motor battery with great performance.

Pros
  • 2-year warranty.
  • High capacity of 103 Ah.
  • Really low price when compared to other AGM marine boat batteries.
  • You can use up to 82.4 Ah when deep cycling.
  • High C-rate of C10.
Cons
  • The casing is not specially designed for marine applications.

7. ExpertPower 12V 20Ah Lithium LiFePO4 Deep Cycle Rechargeable Battery – Lithium Marine Battery

Type: Deep cycle | Size: 7.1 x 3.00 x 6.60 in | Weight: 5.8 lbs. | Group size: N/A | Operating voltage: 12.8V | Technology: LiFePo4 | Capacity: 20 Ah | Operating amperage: 20 Ah at C0.66/10 seconds at 80 amps | Maximum depth of discharge: 100% | Warranty: 1 year
ExpertPower 12V 20Ah Lithium LiFePO4 Deep Cycle Rechargeable Battery | 2500-7000 Life Cycles & 10-Year lifetime | Built-in BMS | Perfect for RV, Solar, Marine, Overland, Off-Grid Applications
  • LiFePO4: ExpertPower’s newest line of batteries – The No.1 Sealed Lead Acid Battery Seller on Amazon.
  • Longer Service Life: Our LiFePO4 battery provides 2500 - 7000 cycles & a 10 years lifetime compared to 200 - 500 cycles & a 3 years lifetime in typical Lead Acid chemistry.
  • Efficient Power: Our LiFePO4 battery’s flat discharge curve holds above 12V for up to 95% of its capacity usage providing astronomical boosts in run-time compared to only 50% in Lead Acid.

The ExpertPower EP1220 Lithium marine battery is one of the lightest models available. This LiFePo4 marine battery has a relatively low capacity but an excellent C-rate and a 100% DOD.

The battery has an installed capacity of 20, Ah and it provides a steady discharge current of 30 amps. The battery can also give up to 80 amps for 10 seconds.

Pros
  • Great price considering its technology
  • Max steady current of 30 amps
  • Maximum DOD of 100%, even though we recommend you go as low as 80% to extend its life span
Cons
  • Very small capacity
  • Only 1-year warranty

What to Consider When Buying a Marine Battery – Buyer’s Guide

Whether you are trying to get the best battery for outboard motor boats, trolling motorboats, or any other marine application, it is important to know what to look for. In this buying guide section, we go over some important aspects that you should consider when choosing a battery. This will help you choose the best marine battery to suit your needs.

What Battery Capacity and C-Rate Do You Need?

The battery capacity determines how much energy you have available to power electric motorboats, accessories, and other devices with only one charge. The C-rate defines how much electrical current can be provided by a battery during a period of time. Generally, C-rates are given in terms of 20 or 10 hours. The electrical current provided at those rates gives you a reference of how much electrical current a single battery can give you. The higher the current, the faster the battery will discharge.

You might want to estimate the load and time of usage required from the battery in relation to the devices installed on your boat. With this list, you can do an estimation to choose the best battery for you.

EXIDE Technologies
Marine Battery Training Guide: How to Select, Install, and Maintain a Marine Battery. Source EXIDE Technologies

What Is the Right Voltage for Your Boat?

Most motorboats require a 12V deep-cycle marine battery to properly function and power all installed devices. In some cases, high-end motors might require a 24-volt marine battery. You can install a battery with that voltage or get two quality 12V marine batteries and install them in series to get the proper voltage.

What Is the Right Weight and Size for Your Battery?

The weight and size of your battery usually refer to the marine group size. You can decide beforehand the battery for your boat or choose the specifications of the battery and consider if the size properly fits. Small boats like kayaks, trolling motors, and other similar boats might require lightweight and compact batteries.

Does It Work Well as a Starter Battery?

The battery you choose should provide the proper current or cranking amps to start the alternator engine or electric motor of your boat. This is why it is important to check the CCA, MCA, or PHCA when choosing a battery for your boat. The meanings of these acronyms are as follows:

  • CCA – Cranking amps for 30 seconds at 0ºF
  • MCA – Cranking amps for 30 seconds at 32ºF
  • PHCA – 5-second pulse of hot cranking at 80ºF

How Fast Can You Charge the Battery?

The charging speed for your battery depends on the parameters set by the manufacturer. The best thing you can do to properly charge your battery is to get a marine battery charger that allows you to set the right charging parameters. By doing this, you will be extending the life span of your battery.

Most batteries on the list vary their charging currents from 10 amps to 30 amps. Considering an 80% DOD, this means a charging time of 480–120 min for 100Ah batteries, 240–80 min for 50Ah batteries, and 90–30 min for the 20Ah battery.

Which Battery Technology Do You Prefer?

The battery technology you choose will determine the advantages you get from it. Lithium batteries have excellent capacities, C-rates, and DOD, but they are also more expensive. Marine AGM battery options provide good discharge currents, have high capacities, and have the best performance–cost relation. Gel batteries have longer life spans than AGM models but are more delicate when charging. Wet cell battery models are robust, resistant to high currents, and have high capacities, but they require regular maintenance, have low DOD, and have shorter life spans.

Do You Know How to Take Proper Care of the Battery You Are Choosing?

Some batteries are more delicate than others. You should always properly charge a battery using a marine battery charger and only store it when it is fully charged. If you do not use your boat for long periods, check the battery every few months to check if it is properly working, and always remember to charge the battery before using your boat again as they can self-discharge over time if not used.

Conclusion

Marine batteries are specially designed to power the motor of your boat and some other devices that you might install on your boat. These batteries will provide you with hours of fun when angling, enjoying a good time at sea, or doing any other activity with your boat.

To have a carefree experience when navigating, it is important to have a strong and reliable ally to power up your boat. In the marine battery reviews section, you will find the best batteries available to pick from. To know what the best marine battery is for your boat, you can use the buying guide. This will help you choose a marine battery that covers all the power needs for your boat.

Best Selling Marine Batteries

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