Your boat's batteries are usually stored in a hidden compartment, out of sight. They play a vital role in keeping your boat running smoothly—until they stop working. In such cases, it's important to know the type and number of batteries you need. Choosing the right battery for your boat is crucial, but how can you determine if you have the appropriate one?
Many boats typically require two types of marine batteries: a starting battery and a deep-cycle battery. The starting battery is essential for firing up the engine, while the deep-cycle battery powers lights, navigation systems, and other equipment. Always consult your engine manual for specific battery recommendations, as using the wrong battery can harm your boat. A suitable battery not only ensures reliable engine starts but also provides consistent power for your essential systems. Since different batteries are designed for specific functions—such as starting the engine or powering accessories—the type of battery, along with its capacity and usage requirements, significantly influences your choice.
In this article, we will explore the different types of marine batteries, marine battery chemistry, and tips you can follow for your batteries.
Marine Battery Types
Selecting the appropriate battery for your boat can help extend its lifespan, enhance user safety, and give you the confidence you deserve during every outing, whether you're fishing offshore or enjoying a day cruising on the water.
Starting Batteries:
Your starting batteries (commonly known as boat cranking batteries) have a sole purpose: to fire up your engine. When you start the ignition sequence, the system sends out strong bursts of electricity for a few seconds. Afterward, the engine’s alternator quickly recharges this electricity.
It’s important to note that these bursts are not used to power electronics, lights, or other devices.
Deep Cycle Batteries:
Your deep cycle batteries are essential for keeping your boat operational. They provide power to your lights, navigation tools, fish finders, trolling motors, and more. These batteries ensure that your boat runs smoothly throughout your trip. Designed to fully recover after extended discharges, your deep cycle batteries can withstand longer usage without being damaged, unlike starting batteries, which can be ruined by similar use.
Dual Purpose Batteries:
If you are looking for one battery that can both power up your boat while keeping everything running, look no further than a dual-purpose battery. A dual-purpose battery works well for smaller boats, but it drains faster than deep-cycle batteries. While it is a good choice for many smaller vessels, be aware that it may not provide enough power to start engines over 200 hp.
Marine Battery Chemistry
When selecting a marine battery for your boat, it’s important to consider the chemical composition. There are four main types of marine batteries: wet cell (flooded), gel cell, absorbed glass mat (AGM), which are all lead-acid batteries, and lithium batteries. The type you choose should depend on your specific needs, such as whether you require it for engine starting or deep cycle use. Additionally, factors like capacity, lifespan, and budget also matter.
Lead-acid Batteries
Commonly known as a wet-cell or flooded battery because the electrolyte is in a liquid state. Lead acid batteries emit gasses that can corrode nearby metal surfaces. If you plan to use a lead-acid battery, it's essential to ensure proper ventilation in the battery compartment to prevent the buildup of explosive gasses.
AGM Batteries
In contrast, Absorbent Glass Mat (AGM) batteries do not have this issue and deliver significantly better performance. They have lower internal resistance, which means they can provide more starting power and accept a charge quickly—up to 45 percent of their total capacity. AGM batteries recharge faster than many deep cycle batteries. They also last a long time, have a low self-discharge rate of just three percent, and perform well. This makes AGM batteries a great choice for boaters who need quick recharging, reliable starting power, and dependable deep cycle performance.
Lithium batteries
Lithium Batteries are a modern option for powering your boat, but they come at a higher cost because each battery requires a separate charging bank that must be isolated from the others. To use this technology effectively, you need to rethink how you manage your boat’s battery system. Unlike traditional flooded or AGM batteries, which can only discharge safely up to 50% of their capacity, Lithium batteries can discharge up to 80%. This means you get 60% more usable power. They also recharge faster and are less than half the weight of traditional flooded or AGM batteries.
While a typical Group 31 AGM battery lasts around 500 charge/discharge cycles, Lithium Iron Phosphate batteries can last up to 3,500 cycles. However, keep in mind that lithium batteries can’t easily be combined or set up in series, making them less suitable for uses like trolling motors or similar systems.
Gel Batteries
Gel batteries have many advantages over traditional flooded batteries. They are sealed and valve-regulated, losing only 3% of their charge each month, and they have a long lifespan with many charging cycles, and do not need maintenance.
These batteries are safe to use because they do not spill, leak, or break easily. They can even be submerged in water. A built-in valve keeps slight pressure inside the battery and releases extra pressure safely when needed. The design reduces gas production, which makes gel batteries safer for use around people and sensitive electronics, although they still need proper ventilation.
Since they are sealed, gel batteries are made to very high standards. However, they must be charged with smart chargers to avoid damage and work properly.
Fun Fact: More than 98% of lead from batteries is recycled, making lead-acid batteries the most recycled consumer product! This significantly surpasses the recycling rates of aluminum cans (55%), newspapers (45%), glass bottles (26%), and even tires (26%).
Battery Tips:
Use only one type of battery chemistry (flooded, gel, or AGM) to avoid undercharging or overcharging due to differing voltage requirements.
Never mix old and new batteries in the same bank, as older batteries can compromise the performance of newer ones.
Regulate charge voltages based on battery temperature to extend battery life and improve charging efficiency. Your charging system should provide 25% to 40% of the total capacity of your battery bank for optimal performance.
Keep your batteries clean, cool, and dry. Check the connectors regularly to make sure they are working well.
For flooded lead-acid batteries, add distilled water when needed. Don't leave them discharged, as this can damage their capacity.
Disconnect your battery when not in use.
Regardless of the battery chemistry you choose—be it AGM, flooded, or gel—you should adhere to your manufacturer’s recommendations for optimal performance.
If you need assistance selecting a battery or require installation services, contact The Mobile Mariner. We are dedicated to providing quality boat maintenance and repair services at your home, dock, or slip.
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