Choosing The Perfect Boat Battery: What You Need To Know

Choosing the right boat battery is essential to ensure a safe and fun trip out on the water. The type of battery you need depends on the purpose of your boat and its engine specifications. There are three main types of marine batteries: starting batteries, deep-cycle batteries, and dual-purpose batteries. Starting batteries provide an initial burst of power to turn over your engine and are best for powering motors and accessories. Deep-cycle batteries, on the other hand, provide long-lasting power and are used for trolling motors, live well pumps, and other electronics. Dual-purpose batteries serve as an in-between option, providing both cranking power and the ability to power additional applications. When selecting a marine battery, it's crucial to consider factors such as battery capacity, type, and input voltage. Additionally, the ambient outdoor temperature of the environment you'll be operating your boat in can affect the type of charger you need. By taking these factors into account, you can choose the right battery to meet your specific power needs and ensure optimal performance on the water.

Battery purpose: starting, running electronics, or both?

Marine batteries are designed to power everything from your boat's engine to electronics and accessories. There are three main types of marine batteries, categorised by their purpose: starting, deep-cycle, and dual-purpose.

Starting batteries, also known as cranking batteries, are designed to deliver short bursts of power to start your inboard or outboard engine. They are not intended for extended, continuous use. If you're using a smaller boat with minimal accessories, a single starting battery may suffice.

Deep-cycle batteries, on the other hand, are built to provide consistent power over a long period, making them ideal for running electronics, trolling motors, fish finders, and other appliances. They are specifically designed for applications that require continuous power delivery. Deep-cycle batteries are commonly used to power various electrical systems and devices on boats, such as lights, radios, and refrigerators.

Finally, dual-purpose batteries aim to provide the best of both worlds. They deliver the initial burst of power needed to start the engine and the sustained power required to run onboard electronics and accessories. Dual-purpose batteries are a good option if you need both functions but don't want to invest in two separate batteries. However, keep in mind that dual-purpose batteries won't perform each task as efficiently as specialised batteries.

When choosing the right type of battery for your boat, consider factors such as boat size, power needs, and the type of electronics and accessories you'll be running. If you have a small boat with minimal electronics, your power requirements will be different from those of a larger vessel with sophisticated systems. Additionally, consider the climate you'll be boating in, as Cold Cranking Amps (CCA) and Marine Cranking Amps (MCA) ratings indicate how well a battery can crank an engine in low-temperature conditions.

Battery capacity (Ah rating)

Battery capacity, or Ah rating, is a crucial specification to consider when choosing the right boat battery. Ah, or ampere-hour, is a unit of electric charge that indicates how much energy a battery can store. It represents the amount of current a battery can deliver over a certain period, typically 20 hours, until it is fully discharged.

When selecting a boat battery, it is important to match the battery capacity to your power requirements. This includes considering the engine size, type, and ambient temperature. For example, larger engines or those operating in colder temperatures may require higher cranking power and, consequently, a larger battery capacity.

Additionally, you should assess the electrical loads on your boat. If you have numerous power-hungry electronics and accessories, you will need a battery with sufficient capacity to meet those demands. Deep cycle batteries, for instance, are designed to provide a smaller amount of energy over an extended period and are suitable for powering electronics. On the other hand, starting batteries deliver high bursts of power for short durations to crank the engine.

It is recommended to have two battery systems on boats: one for engine starting and the other for auxiliary or house battery requirements. For engine starting, you can calculate the required battery capacity by multiplying the engine's cubic inches by the recommended cranking amps per cubic inch for the fuel type. For gasoline engines, a good rule of thumb is 1 cranking amp per cubic inch, while for diesel engines, it is typically 2 cranking amps per cubic inch.

For auxiliary or house battery requirements, determining the necessary battery capacity involves calculating your total watt-hours needed. This is done by multiplying the wattage draw of each device by the expected usage time and then summing up the values for all devices. It is advisable to select a battery with a capacity higher than your baseline watt-hour usage to accommodate any fluctuations in power demands.

Battery size (physical dimensions)

When choosing a battery, it's important to consider how it will be used. For example, will it be used for starting an engine, or for powering "house" loads, or perhaps both?

In addition, the weight of the battery is also a factor to consider. You want to choose a battery with an average weight so that you can easily move it in and out of the boat.

Another factor to consider is the battery's output, which is measured in marine cranking amps (MCA). MCA is the number of amps a battery can deliver for 30 seconds at 0°F while maintaining its voltage above 7.2 volts. This is important for knowing if you'll have enough power to start your engine in cold conditions.

When it comes to engine starting requirements, the battery size will depend on the type of engine you have. For gasoline engines, a good rule of thumb is to have 1 cranking amp per cubic inch, while for diesel engines, you'll need 2 cranking amps per cubic inch.

Don't forget to also consider the physical dimensions of the battery when choosing a marine battery. By taking into account the space available in your boat and the size of the battery, you can ensure a proper fit.

Battery weight

Lithium-ion batteries are known for their lightweight and high-energy density, making them a powerful option that can reduce the load on your boat's engine. They also have a long lifecycle, making them a good choice for those who want to avoid frequent replacements. Lithium-ion batteries can also be discharged up to 80% of their capacity, providing 60% more usable power than other types of batteries.

Another option is Absorbent Glass Mat (AGM) batteries, which are completely sealed and can be mounted in various positions. AGM batteries are also lighter than lead-acid batteries, making them a weight-saving option for your boat. They also recharge faster, last longer, and have a higher power output than flooded battery options.

When considering battery weight, it is also important to think about the application of the battery. If you need a battery for engine starting, a starting or cranking battery is recommended. These batteries provide high bursts of power for short periods to kick over your engine. On the other hand, if you need a battery to power onboard electronics and accessories, a deep cycle battery is more suitable as it provides a smaller amount of energy for a longer period.

Battery output (MCA, CCA, reserve capacity)

Marine Cranking Amps (MCA) and Cold Cranking Amps (CCA) are two vital metrics that help gauge a battery's ability to start a boat's engine. MCA is similar to CCA but is measured at a higher temperature of 32°F (0°C) instead of 0°F (-18°C). MCA ratings are generally 20-25% higher than CCA ratings and are more relevant for marine applications. A higher CCA rating is crucial for reliable engine starts in freezing conditions.

When selecting a starting battery, it is important to consult the boat engine manufacturer's guidelines for the minimum recommended CCA or MCA ratings. Choosing a battery that meets or exceeds these recommendations ensures the battery can deliver the required power to start the engine reliably.

If you plan to use your boat in colder climates, the CCA rating becomes more critical. Opt for a battery with a higher CCA rating to ensure reliable engine starting in low-temperature conditions. Conversely, if your boat is primarily used in warmer environments, the MCA rating will be a more suitable indicator of the battery's performance.

In addition to CCA and MCA ratings, it is crucial to consider a battery's reserve capacity. Reserve capacity indicates the number of minutes a fully charged battery can deliver a constant current of 25 amps at 80°F (26.7°C) before its voltage drops below 10.5 volts. This metric is essential as it provides an indication of the battery's ability to power your boat's electrical accessories in an emergency, such as when the engine or charging system fails.

Frequently asked questions