outboard motor boat

What Is the Best Marine Battery and How Do You Choose?

Reliable batteries are an important piece of equipment on board your boat. If they fail and you’re miles out at sea, you can’t just run to the store and pick up a new one!

The marine battery you choose will depend on the purpose of the battery as well as your priorities. Each type of battery comes with its pros and cons so you’ll need to decide what best fits your needs. 

Let’s look at marine battery applications as well as the most common types to help you decide. If you don’t know which car to purchase, make sure you are looking at your best options

The Function of Your Marine Battery

There are a couple of different applications for batteries onboard a boat. Let’s learn about them here.

Starting Batteries

First up, you need a battery to store energy for starting your engine. Engines need energy to start and that doesn’t come from thin air!

You can think of starting batteries like sprinters. They are designed to give a burst of power for a short period of time.

The range of amperes is considerable, depending on the size necessary for your engine. In general, starting batteries give a burst of power for 5-15 seconds of anywhere between 75 and 400 amps.  

After this burst of power, the engine’s alternator begins to recharge the battery in short order. Deep discharges significantly reduce the lifespan of this type of marine battery. 

Deep Cycle Batteries

If starting batteries are sprinters, then deep cycle batteries are marathon runners. These batteries house the energy necessary to power your boat when the engine (and other sources of power like shore power charge, wind or solar power, etc.) are not available.  

They give off a steady stream of power over a longer period of time. You can also more fully discharge these batteries without affecting their lifespan. Depending on the type of battery you can discharge between 50 and 100% of the stored power. We’ll get into that a bit more in a minute. 

When choosing the batteries for your bank, always choose more storage capacity than you actually need. Aim for about three to four times the amount of energy you expect to use before recharging. 

Dual-Purpose Batteries

Dual-purpose batteries are what you’d expect. They can do the work of the starting battery as well as house energy for more long-term use. They do this job well but do not excel at either function as well as a dedicated starting or deep cycle battery does. 

However, they are excellent for use in certain situations including:

  • On sailboats with two identical batteries
  • On small powerboats that only require one battery
  • On small boats with only one battery bank
  • Will last longer as a starting battery and be more reliable

Larger boats with heavier power needs will generally benefit from having a dedicated starting battery as well as a bank of deep cycle batteries to provide running energy.

Types of Batteries

Once you decide on the function you need the battery to perform, it’s time to decide on the type of marine battery you should buy. Three main types are available. Let’s look at the pros and cons of each.

Lead-Acid Batteries

Lead-acid batteries are like the batteries that you find in your car. However, these batteries are sealed to prevent the acid from spilling with the motion of the boat.

These used to be the most commonly found type of batteries on a boat. They were readily available and (relatively) inexpensive. However, there are other options nowadays that are a bit better.

Lead-acid batteries can give off toxic fumes and improper disposal poses a threat to the environment. They also require frequent watering to keep them in tiptop shape. You also shouldn’t discharge them more than 50% as any more than that can negatively affect their lifespan. 

AGM Batteries

AGM batteries are a bit lighter than lead-acid batteries and don’t have any toxic liquids or fumes that you have to worry about. They are excellent for cranking engines in cold temperatures which can be important depending on the location of your boat.

They also tend to charge more quickly than comparable lead-acid batteries and hold their charge better. However, to preserve their lifespan they also shouldn’t be discharged more than 50% and you have to be careful not to overcharge them. 

Lithium Batteries

Lithium marine batteries are the best of the bunch. They are far lighter and smaller than either lead-acid or AGM, leading to significant weight and space savings. They also require no maintenance and last about 2,000 cycles as compared to about 1,000 cycles for an AGM battery. 

They can be discharged 100% between charging cycles, although keeping it above 80% will promote the longest lifespan. 

So why doesn’t everyone have lithium batteries on their boat? The cost of them scares off a lot of people. 

However, as technology has improved, the price of these batteries has come down. Plus, people are realizing that while the upfront cost is a bit higher, lithium batteries can actually be cheaper in the long run. Not only can they tolerate more recharging cycles, but also they provide more power in each cycle because you can discharge them more. 

Plus, with no toxic liquids or fumes, they are better for the environment and better for the people who will be breathing the air aboard your boat.

The Right Marine Battery for Your Boat

The bottom line when it comes to choosing a marine battery is to get what works for your needs. Smaller boats and sailboats may only need one or two dual-purpose batteries. 

Larger boats can benefit from starting batteries and a bank of deep cycle batteries. The more time you plan to use your batteries between recharges, the larger a bank you will need to store enough power. 

We hope this resource has been helpful. Be sure to check out more of our articles for all your tech needs!