Boat Batteries: Understanding Marine Power Sources

Marine batteries are designed to withstand the unique challenges of the marine environment. There are four main types of marine batteries: starting, deep cycle, dual-purpose, and lithium. Starting batteries, also known as cranking batteries, provide a short burst of power to start the engine. Deep cycle batteries provide a steady power supply over a longer period, powering electronics and accessories. Dual-purpose batteries combine the functions of starting and deep cycle batteries and are ideal for small vessels. Lithium batteries are the newest type, offering longer lifespans and faster charging than traditional lead-acid batteries. When choosing a marine battery, factors to consider include usage, capacity, size, weight, maintenance requirements, and budget.

Boat battery types: Flooded lead acid, gel, AGM, and lithium

Marine batteries are responsible for any electrical process on your boat, from the trolling motor to GPS, radios and more. Boat batteries are designed to supply higher bursts of energy and withstand the forces of the water.

There are three basic types of marine battery: starter, deep cycle, and dual-purpose.

Flooded Lead Acid Batteries

The most common type of deep cycle battery, these are also known as "wet cell" batteries. They are the most cost-effective upfront, but require periodic inspection and maintenance. They are the bulkiest and heaviest, weighing between 60 and 80 pounds, and have a shorter lifespan of around 2-4 years. They are also the slowest to charge.

Gel Batteries

These are a type of FLA battery. They are sealed, so there is no need to top them off, and they don't leak. However, they are still heavy and bulky, and relatively expensive. They are also less durable and have a shorter lifespan than AGM batteries.

AGM (Absorbed Glass Mat) Batteries

AGM batteries are a maintenance-free alternative to traditional flooded lead-acid batteries. They are used in everyday cars and trucks, as well as motorcycles, military vehicles, aircraft, and submarines. They can be installed at any angle and are sealed, non-spillable, and maintenance-free. They are more expensive due to high manufacturing costs and are sensitive to overcharging.

Lithium-Ion Batteries

Lithium batteries are a relatively new entry to the marine market, but they are a rising choice for boaters. They are smaller, lighter, long-lasting, and faster-charging than lead-acid batteries. They are also safer and won't leak. However, they are the most expensive option, costing four or five times more than lead-acid batteries.

In summary, AGM and lithium batteries are becoming more popular than flooded and gel batteries due to their efficiency, low maintenance, and reliability.

Starting batteries: Power the engine

Starting batteries, also known as boat cranking batteries, have a single purpose: to start the engine. They discharge high-amperage current bursts for several seconds when you turn on the ignition, and are then quickly recharged by the engine's alternator. They are not used to run electronics, lights, or other equipment.

Starting batteries are the sprinters of your electrical system. They deliver between 75 and 400 amperes for 5 to 15 seconds and are then rapidly recharged by your engine's alternator. Like all lead-acid batteries, they are constructed with alternating layers of negative and positive plates with insulation between them.

Starting batteries have thinner and more numerous plates, providing extra surface area to generate high-amperage bursts of current. However, the plates are relatively fragile in high-impact environments, and starting batteries do not tolerate deep discharges, which reduce their operating lifespan.

When choosing a starting battery, consider the amount of power needed to crank your engine. The two common power measurements are CCA (Cold Cranking Amps) and MCA (Marine Cranking Amps). CCA measures the number of amps a battery can deliver for 30 seconds at 0°F while maintaining a voltage above 7.2 volts. MCA is similar but measured at 32°F. Batteries work better at higher temperatures, so MCA is 20-25% higher than CCA. Engine size, type, and ambient temperature will also determine the size of the cranking battery you need.

There are several types of starting batteries available, including flooded lead-acid, gel, AGM (Absorbed Glass Mat), and lithium-ion. Flooded lead-acid batteries are the least expensive option, but they require more maintenance and have a shorter lifespan than other types. Gel and AGM batteries are sealed and maintenance-free, but they are more expensive and have a limited lifespan. Lithium-ion batteries are smaller, lighter, longer-lasting, and faster-charging, but they are also the most expensive option.

Deep cycle batteries: Power electronics

Deep cycle batteries are designed to be regularly discharged and recharged. They are the "marathon runners" of the storage system, providing sustained power with low current draw over extended periods. They are ideal for cyclic applications where the user tells the battery when it needs to be used.

Deep cycle batteries have thicker plates than starter batteries, allowing them to provide steady, consistent power. They can be charged and discharged for many cycles, making them perfect for powering electronics such as trolling motors, lights, GPS, fish finders, and more.

There are several types of deep cycle batteries:

• Flooded Lead Acid Batteries (FLA): These are the most traditional type. They require ventilation to disperse hydrogen gas produced during overcharging and need regular monitoring and maintenance. They are also bulky and heavy.
• Sealed Lead Acid Batteries: These come in various forms, including Absorbed Glass Mat (AGM) and Gel cells. They are often maintenance-free and offer flexibility in mounting options. Gel batteries are resistant to extreme temperatures, shock, and vibration, while AGM batteries have a lower internal resistance.
• Lithium-ion Batteries: Lithium-ion batteries have high energy density and are a preferred choice for those looking for a reliable battery investment. They are smaller, lighter, long-lasting, and faster charging than lead-acid batteries.
• Deep Cycle Gel and AGM Batteries: These are subcategories of SLA (sealed lead acid) batteries. Gel batteries use a substance that turns the electrolyte acid into a thick gel, making it non-spillable. AGM batteries use a glass mat to keep the electrolyte in place, optimising the surface area of the plates for better distribution.

To ensure optimal performance and longevity of deep cycle batteries, proper maintenance is essential. This includes regular charging, checking water levels, keeping the battery clean and dry, avoiding over-discharging, and using a suitable charger.

Dual-purpose batteries: Combine starting and deep cycle functions

Dual-purpose boat batteries combine the functions of starting and deep cycle batteries. They are a good fit for smaller vessels, saving space, weight, and money. However, they drain quicker than deep cell batteries and may not have the capacity to crank engines exceeding 200 hp.

Dual-purpose batteries have larger, thicker plates containing more antimony than starting batteries, and an active lead paste chemistry. They can tolerate deep discharges that would ruin a typical starting battery. However, they have lower storage capacity than comparably-sized deep cycle batteries.

Dual-purpose batteries are ideal for runabouts or other small powerboats using a single battery for both starting and running loads with the engine turned off. They are also suitable for sailboats with two identical batteries used interchangeably for starting and house electrical loads, as well as boats with one battery bank that does double duty for house applications and engine starting.

When choosing a dual-purpose battery, consider the performance you desire and your budget. While dual-purpose batteries are a good compromise, they may not provide enough power to start certain engines or last as long as typical deep cycle batteries.

Battery maintenance: Charging, cleaning, and storage

Boat batteries can be left dormant for weeks or months, so it's important to keep them properly charged and maintained. Here are some tips for charging, cleaning, and storing your boat batteries:

Charging

• All batteries will self-discharge if left unused. A lead-acid battery may lose 5% of its charge per month, so periodically charge batteries that are not in use to bring them up to full capacity.
• How a battery is charged is critical to its health and longevity. Both overcharging and undercharging will reduce the battery's lifespan and degrade its performance.
• Use a marine smart battery charger designed for permanent installation. These chargers can be safely left connected to the batteries and will automatically reduce the charge to avoid overcharging.
• Better chargers offer three-stage charging: bulk, absorption, and float. These stages will keep the battery in its best condition and ensure it's not overcharged.
• Flooded lead-acid batteries should have their electrolyte levels topped up with distilled water, not tap water.
• Batteries can be charged from multiple sources, including engine alternators, shore-power chargers, solar panels, and wind generators.
• When using solar panels or wind generators, use a smart regulator in the circuit to protect the batteries and ensure a proper charge.
• Always follow the manufacturer's recommendations for charging and maintaining your batteries.

Cleaning

• Keep the battery compartment well-ventilated. Gases escaping from the battery, especially overcharged lead-acid batteries, can be explosive.
• Clean the tops of the batteries as part of routine servicing. A dirty battery can self-discharge to the ground under certain conditions.
• If white powder builds up on the terminals, clean it off with a baking soda solution to neutralize any acid.
• When working around batteries, wear gloves and protective clothing to protect yourself from battery acid.

Storage

• Perform regular maintenance, including watering and removing corrosion.
• Before storing for winter, charge the batteries one final time. This ensures they will completely recharge next season and reduces the risk of freezing.
• Disconnect the negative cable and check the specific gravity or voltage after a few hours.
• Disconnect the terminals to remove all electrical loads from the batteries. Electronics have small parasitic loads that, combined with battery self-discharge, can damage batteries in storage.
• Remove the batteries and store them in a cool, dry place where they won't freeze. Wood surfaces in garages or storage facilities are recommended.
• Store batteries somewhere accessible to make charging easier.
• Use the correct charger for your battery type. Flooded and AGM batteries often require different chargers and algorithms.
• Trickle-charge batteries or charge them monthly to prevent self-discharge and extend their lifespan.

By following these maintenance, charging, cleaning, and storage tips, you can keep your boat batteries in good condition and ensure they're ready for use when you need them.

Frequently asked questions