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How to Choose the Best Marine Battery

If you've recently purchased a used boat or are preparing your boat for the upcoming season, you probably have a maintenance to-do list to take care of before you feel confident about heading out on the water. One of those items most likely involves checking or replacing your vessel's battery.

If this is the first time you find yourself having to replace the battery, there are some things you should be aware of before you complete your purchase. There are different types of batteries for different tasks on the boat and you will need to ensure you find a battery that meets your power needs. This article will discuss some basic marine battery information and by the time you are done with this article, you will feel confident about purchasing the right battery fit for you and your boat.

Marine batteries have two tasks, starting and powering electrical loads. You can purchase a separate battery for each job or there may be an option for you to purchase one single battery to do both. The amperage required for your vessel will need to be determined, as well as what loads you will be placing on the battery. The size of the battery is also important as vessels require specific battery sizes to be installed per manufacturer directions.

Basically, you want the most reserve capacity you can get but may be limited due the boat's ability to accommodate a larger battery. Batteries also come in three styles, flood lead acid, AGM and gel. Each performs a little differently, but the main differences are in the maintenance requirements for each. Flood acid batteries require vigilance and are susceptible to leaks. They must be checked and filled with distilled water as necessary and should be checked with a hydrometer to measure the amount of sulfuric acid in the electrolytes. This is important to determine the charging efficiency of the battery. This is a great, long lasting battery and a good economical choice.

AGM and gel cell batteries are considered maintenance free. They can be installed on their sides if necessary as there is no danger of fluid leaking from the battery. These batteries do not require regular filling with water, they are self-contained. Gel batteries are not used as much anymore and are usually replaced with an AGM style.

Maintenance free does not mean the battery does not need to be inspected and cared for, you will still need to keep it charged in times when the boat is not in use and check terminals and ventilation on a regular basis. Battery life is determined by the number of cycles it goes through and how good the unit is at withstanding frequent discharges. How much the battery is discharged, percentage-wise, with each use will also impact how long it lasts. Discharging a battery completely down to zero will render it incapable of being recharged and worthless.

Starting Batteries Defined Starting or cranking batteries have only one job, to start the engine of the boat. They are designed to give off short, high bursts of power. These batteries have a lot of lead plates and they are thinner than they would be in other types of batteries to ensure a quick recharge time. Your boat's engine specs will dictate how many CCAs (cold cranking amps) you will need. Starting batteries are not useful in putting out deep discharges and will not last very long if that is the case.

Cold cranking amps are the number of amps a battery can put out at 0°F for 30 seconds. If the battery lists MCAs, marine cold cranking amps, this is the same measurement except tested at 32°F. These batteries are good choices for outboards and smaller vessels.

Deep Cycle Batteries Defined Deep cycle batteries are made to handle the electrical load of the accessories on your vessel. Lights, fish finders, radios, etc. are all powered by the deep cycle. This battery type is characterized by thick lead plates that are optimum for storing or banking power for later use. The deep cycle will run accessories on its own power even if not being charged by the alternator or another power source. Cruiser vessels will require one or more powerful batteries like this to provide for the electrical equipment on board. The battery is rechargeable and once discharged and power is full again, it is ready to go once more. Dual Purpose Batteries Defined The dual purpose battery is just what it sounds like - it is capable of handling both starting duties and powering accessories. The dual purpose does not have as much storing capacity as the deep cycle, however, so this may be a factor for you when deciding which type of battery works for you. These are a good option if you do not discharge your battery below 50%. If you do tend to do that regularly, then a deep cycle is the better choice. A dual purpose would be good for sailboats with identical interchangeable batteries.

Which One Do You Need? When determining which battery is the best fit for your boat, look at the variety of issues mentioned in the above. Check your manufacturer's specs to be certain you choose a battery that meets at least the minimum requirements. Cold cranking amp ratings are going to be a factor for your starter battery. The amount of room you have to install the battery will limit how big a battery you can fit in the battery compartment. Do a run through of all the accessories on the boat, and if you have a lot of electrical options and add-ons, then be sure to purchase a battery with enough storage capacity to run all those electrical gadgets.

One thing to check for is the rating of the deep cycle batteries. You will see 20hr capacity ratings noted on the battery. This is a standard unit of measurement for battery storage capacity. All deep cycles are noted with this and it indicates how long it took to fully discharge the battery over a 20 hour period. This ensures that a universal measurement system is being used so that when you are considering batteries, you are comparing "apples to apples", so to speak. (ex. A rating of 100AH @ 20HR means the battery is totally discharged in 20 hours running a 5 amp load.)


When looking for a new battery, do not be tempted to purchase an automotive battery for your boat. Though they may look similar, the internal design and components of these batteries are very different and using a car battery is bound to leave you stranded pretty quickly.

Installation is important. You want to protect your investment. Make sure you have a sturdy plastic box for mounting the battery to protect it. The battery needs to be well ventilated to prevent the build-up of gasses. Nothing should be laid on top of the battery and connections should be secure and checked frequently. Be careful and do not assume that all sealed batteries can be laid on their sides for mounting, some still have a danger of leaking. Check with each manufacturer regarding the mounting capabilities of your battery.

There are different options for purchasing batteries. You can choose to buy locally at a marine supply or auto parts store. Online shopping provides convenience and an almost unlimited selection. There can be a significant difference between suppliers on retail pricing, so make certain that you price shop.

By M Ristagno


  • sc0ttsr

    Great Article. Thank you.

    13:30 06 Oct 2016
  • RobertStein

    You have done a good job covering lead acid batteries. I'm not a boat person and perhaps lithium (LiFe) batteries are not permitted on boats; but if they are they are a great option offering many advantages over lead acid. Amazon has a wide selection. Hope this is helpful.

    20:01 30 Jan 2024

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