Choosing The Right Boat Battery: West Marine Guide

Marine batteries are essential for boating, powering everything from the engine to electronics and accessories. There are three main types of marine batteries: starting (cranking) batteries, deep-cycle batteries, and dual-purpose batteries. Starting batteries deliver quick bursts of energy to start the boat's engine but are not designed for extended use. Deep-cycle batteries provide consistent power over a long period, making them ideal for electronics and appliances. Dual-purpose batteries combine the functions of the other two types but are less efficient. When choosing a battery, it's important to consider how it will be used, the performance desired, and the budget. West Marine offers a range of battery options, including flooded lead-acid, AGM, gel, and lithium batteries, each with its own advantages and disadvantages.

Starting, dual-purpose or deep-cycle battery?

West Marine offers three different types of batteries: Starting, Deep Cycle, and Dual-Purpose.

Starting Batteries

These batteries are designed to crank the starter of your boat's engine. They deliver between 75 and 400 amperes for 5–15 seconds and are then recharged in short order by your engine's alternator. Starting batteries have thinner and more numerous plates, which provide extra surface area to generate high amperage bursts of current. However, the two drawbacks of this construction are that the plates are relatively fragile in high-impact environments, and that starting batteries do not tolerate deep discharges, which reduce their operating lifespan.

Deep Cycle Batteries

Deep cycle batteries are the marathon runners of the storage system. They power the electrical loads on your boat when no charge source (shore power charger, engine alternator, wind generator, or solar panel) is available. Compared to starting batteries, deep cycle batteries recover fully after being heavily discharged over longer periods because their design features thicker plates with a high content of antimony.

Dual-Purpose Batteries

Dual-purpose batteries are a good compromise, tolerating deep discharges that would ruin a typical starting battery. They have large, thick plates containing more antimony than starting batteries and an active lead paste chemistry. Since they have lower storage capacity than comparably-sized deep cycles, they are recommended 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.

Flooded, gel, AGM or lithium battery?

When choosing a battery, you should first consider how the battery will be used. For example, will it be used for starting an engine, or powering electronics?

West Marine offers four different battery types: Flooded, Gel, AGM (Absorbed Glass Mat), and Lithium Iron Phosphate.

Flooded Batteries

Flooded marine batteries are commonly used in starting applications. They have a no-spill design and can be tilted to a 45-degree angle, making them perfect for marine use. They are also the most traditional type of battery and are widely used in cars and standalone energy systems. They are more cost-effective than AGM batteries and have the highest ROI and lowest operating costs.

However, they require periodic inspection and maintenance, and extreme climates can significantly affect their lifespan. They also have the weakest internal construction and some very high internal resistance statistics.

Gel Batteries

Gel batteries are sealed and spill-proof, and they offer advantages over regular flooded batteries. They self-discharge at only three percent per month, handle the highest number of lifetime charging cycles, are maintenance-free, and are leakproof and submersible. They are also manufactured to very high-quality standards.

However, they are extremely sensitive to charge voltages above 14.1 volts DC at 68 degrees, and they should not be used for fast charging/discharging or high-amperage situations.

AGM Batteries

AGM batteries are the latest and greatest in lead-acid batteries. They are maintenance-free and can be installed sideways. They are also the most impact-resistant and have the least internal resistance. They are commonly found in off-grid power systems and electric vehicle services.

However, they often have a higher upfront cost than lead-acid batteries, and users should take care when charging to avoid affecting the battery's life and performance.

Lithium Batteries

Lithium Iron Phosphate batteries are among the most advanced marine batteries in the world. They can be discharged up to 80% of their capacity, which equates to 60% more usable power than other types of batteries. They can also be recharged at a faster rate and weigh less than half of their counterparts.

However, they are very expensive.

In summary, each battery type has its own unique characteristics and performance capabilities. When choosing a battery, it is important to consider your specific needs and budget to determine which type of battery is the best fit.

Battery capacity and your boat's energy needs

When choosing a battery, it's important to consider how you will use it. For example, will it be for starting an engine, powering "house" loads, or both? This will help you determine the type of battery you need (starting, deep cycle, or dual-purpose) and the right battery chemistry (flooded lead acid, AGM, gel, or lithium iron phosphate).

Deep cycle batteries, for instance, are designed to power "house" loads like running lights, electronics, cabin lights, 12-volt appliances, and other loads. To ensure your battery can meet your boat's energy needs, it's recommended to create an "energy budget" and select a battery with sufficient amp-hour capacity and reserve minutes rating.

Amp-Hour Capacity

Amp-hour capacity refers to the total amount of electrical energy a battery can store and supply over a period of time, typically measured in hours. For example, a battery with a 105-amp-hour capacity can theoretically supply 1 amp of current for 105 hours, 2 amps for 52.5 hours, and so on. However, the actual amount of time a battery can supply power will depend on factors such as the amount of current drawn, temperature, and battery age.

When selecting a deep cycle battery, it is generally recommended to choose one with 3 to 4 times your daily energy consumption in battery amp-hour capacity. This helps to avoid damaging deep discharges and reduce recharging time.

Reserve Minutes

Reserve Minutes is an industry standard that defines how long a battery can sustain a load of 25 amps before its voltage drops to 10.5 volts at 80°F. This rating is important to consider when powering "house" loads, as it gives you an idea of how many amps are available to power these loads.

Choosing the Right Battery for Your Boat

When it comes to battery capacity and your boat's energy needs, it's crucial to select a battery that matches your boat's specific requirements. Consider the size of your boat, the power needs of your electronics and appliances, and whether you need separate starting and deep-cycle batteries or a dual-purpose battery.

Additionally, factors such as cold cranking amps (CCA) and marine cranking amps (MCA) are important to consider, especially if you operate your boat in cold temperatures. Reserve capacity (RC) is also crucial, as it ensures your battery can power your systems in the event of an alternator failure.

Battery cranking amps (CCA and MCA)

Cold Cranking Amps (CCA) and Marine Cranking Amps (MCA) are measurements of the power available for cranking a starter. CCA is the number of amps a battery can deliver for 30 seconds at 0°F while maintaining its voltage above 7.2 volts. MCA is similar but measured at 32°F instead of 0°F. The reason that MCA is 20–25% higher than CCA is that batteries work better at higher temperatures. CCA ratings are usually used in the automotive industry, while MCA is a more realistic rating for boats as few boats are used in sub-zero weather.

CCA and MCA are two of the most important factors to consider when choosing a starting battery for your boat. Engine size, type, and ambient temperature determine what size cranking battery you need. High cranking power (and a larger battery) is required for cold temperatures, diesel engines, or large and high-compression gas engines.

If you're replacing an old battery, West Marine recommends that you first check the minimum CCA or MCA stated by the engine or boat manufacturer. If a Group 24, 550 CCA battery worked well for five years, they suggest you replace it with a similar model. If it failed after a season or two, they suggest you look for a battery with a higher CCA or MCA rating.

Battery maintenance and longevity

To ensure your boat battery lasts as long as possible, it's important to follow some basic maintenance tips. Firstly, always use a charger designed specifically for marine batteries. Overcharging or undercharging can reduce the lifespan of your battery. Different types of batteries also require different charging voltages, so be sure to check the specifications for your particular battery. For example, a 12-volt deep-cycle battery should be charged to around 14.4-14.8 volts.

Consider using a trickle charger to maintain battery health when your boat is not in use. This will help to keep your battery charged and ready to go when you need it. If you use your boat infrequently, a maintenance-type battery charger is a good idea to keep the battery fully charged between outings.

Before storing your boat for the off-season, make sure to fully charge the batteries. Then, disconnect the terminals so that nothing can drain the battery. If you have access to power at your storage site, keep the batteries on a battery maintainer/charger during the off-season. Otherwise, remove the batteries from the boat and store them in a cool, dry place where they can be connected to a maintenance charger.

Regularly check the battery terminal connections to ensure they are snug and free from corrosion. Corrosion can prevent your battery from functioning correctly. Clean the terminals using a mixture of baking soda and water if you notice any corrosion buildup.

High temperatures can also shorten the lifespan of your battery, so it's important to keep it cool and out of direct sunlight as much as possible. Vibration can also damage your battery, so make sure to secure it with a good battery box or tray.

Finally, when it comes to battery types, lithium batteries offer the longest lifespan, tolerating deep discharges better than other types. They can be recharged much faster and produce more usable amp hours over their lifetime. However, they are the most susceptible to damage from overcharging, so a compatible charging system is required.

Frequently asked questions