Choosing The Right Boat Battery: What Type To Pick?

Choosing the right battery for your boat is essential to ensure optimal performance and avoid being stranded on the water. The selection depends on various factors, such as the size of your boat, the type of engine, and the power requirements for starting the engine and running electronics or appliances.

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 initiate the engine, while deep-cycle batteries provide consistent power over an extended period for electronics and appliances. Dual-purpose batteries combine both functions but are less efficient than specialised batteries.

When selecting a battery, consider the marine-cranking amps (MCA) or cold-cranking amps (CCA) to ensure sufficient power for engine starting. Additionally, factor in the amp-hours (Ah) rating, which indicates the battery's capacity and how long it can deliver power.

The number of batteries needed depends on the boat's length and the number of engines. Smaller boats under 14 feet may require just one battery, while larger boats with multiple engines will need multiple batteries.

It is also important to choose between different battery chemistries, such as lead-acid or lithium-ion batteries, considering their advantages and drawbacks in terms of weight, maintenance, durability, and cost.

Starting vs. deep-cycle batteries

Marine cranking batteries, also known as starter batteries, are designed to send short and intense bursts of energy to start a boat's engine. They have several thin plates that increase the surface area and make it easier to provide the necessary power. While they are great for cranking an engine, they are less ideal for continuous discharge or "cyclic" use.

Deep-cycle marine batteries, on the other hand, provide a continuous and reliable power output over long periods. They are designed for trolling and running electronics like sonar, GPS, and radios. Deep-cycle batteries have fewer but thicker plates, allowing them to withstand high temperatures and resist overheating. They can be completely drained and recharged frequently, which is not possible with cranking batteries.

While some dual-purpose batteries can work for both cranking and trolling, they do not always allow a vessel to perform optimally. Cranking batteries are engineered to provide a quick burst of power to start the engine, while deep-cycle batteries are designed for continuous power output. Using two separate marine batteries, each specialised for its intended purpose, will generally result in better performance and lower operating costs.

When choosing a marine battery, it is essential to consider how it will be used. For example, will it be used solely for starting the engine, or will it also need to power other electrical systems on the boat? Additionally, factors such as performance requirements, budget, and battery maintenance should be taken into account when making a decision.

Battery size requirements

Engine Starting Requirements

The size of the battery you need for starting your engine will depend on the engine manufacturer's recommendations, the engine size, type, and ambient temperature. You should primarily look at the battery's marine-cranking amps (MCA)—this measures how much power your battery can deliver in a short burst, at 32°F (0°C for Cold Cranking Amps, CCA). For gasoline engines, a good rule of thumb is to have 1 cranking amp per cubic inch; for diesel engines, you'll need 2 cranking amps per cubic inch.

Auxiliary or House Battery Requirements

Answering "what size marine battery do I need" is more complicated when looking at auxiliary or house batteries. Power needs will vary depending on the number and nature of the devices you've got plugged in. Each device draws a certain amount of watts per hour while in use. Multiply this number by the hours or minutes you expect to use the device between battery charges, then add up the total watt-hours needed for all devices. It's a good idea to get a battery larger than your baseline watt usage, in case you exceed your estimate.

Battery Type

The type of battery you choose will also impact the size requirements. For example, if using lead-acid batteries, you would need to double the battery rating to match your energy needs as a discharge deeper than 50% damages these batteries rapidly. In contrast, high-quality lithium batteries can handle deep discharges and complete drainage without a problem.

Boat Size and Power Needs

The size of your boat and its power needs will also impact the size of the battery you require. Smaller boats with minimal electronics will have different power needs than larger vessels with more sophisticated systems.

Number of Batteries

The number of batteries you'll need will depend on the size of your boat and whether you have a single or multiple engines. Boats under 14 feet will only require one battery; boats 15-23 feet with a single engine will need two batteries, and boats 24 feet and above with more than one engine will require three or more batteries, with an additional battery for every extra engine.

Battery types

There are three main types of marine batteries: starting, deep-cycle, and dual-purpose. Starting batteries deliver quick bursts of energy to start the boat's engine but are not designed for extended, continuous use. Deep-cycle batteries, on the other hand, are built to provide consistent power over long periods, making them ideal for electronics, trolling motors, and appliances. Dual-purpose batteries combine the functions of the other two types but are less efficient.

Starting batteries are also known as cranking batteries. They are designed to deliver a large amount of power to start the engine. Once the engine is running, it will recharge the battery, and the battery won't be needed for long-term power.

Deep-cycle batteries are engineered for steady, sustained energy output, perfect for electronics like fish finders, GPS systems, and onboard appliances that need continuous power for long periods.

Dual-purpose batteries are a good option for small boats where space is limited, as they can start the engine and power electronics. However, they are less efficient than specialised batteries and have a lower power capacity than similarly-sized deep-cycle batteries.

Marine batteries are specially designed to handle the challenges of the marine environment. They are fully sealed to prevent leaks and are vibration-resistant. They are also constructed with sturdier frames and elevated electrical connectors to avoid water damage and short circuits.

When choosing a marine battery, you will need to consider the size of your boat and its power requirements. Smaller boats with minimal electronics will have different needs than larger vessels with more sophisticated systems. You will also need to think about whether you need high bursts of power for starting the engine, long periods of power for electronics, or both.

In addition, there are different chemical compositions to consider when choosing a marine battery. The two main types are lead-acid and lithium. Lead-acid batteries are traditional and cost-effective but are heavy, large, and require more frequent replacement. Lithium batteries, on the other hand, are lightweight, durable, and easy to maintain, making them a popular choice for boaters.

Reserve capacity

RC is particularly important if you plan to run electronics off your battery. If your alternator fails, RC will determine how long your systems can continue to function.

When calculating your power needs, you must consider the number and nature of the devices you will be plugging in. Each device draws a certain number of watts per hour while in use. Multiply this figure by the expected hours (or minutes) of use between battery charges. Add up the watt-hours for all devices to determine your total watt-hour usage. It is generally recommended to get a battery that exceeds your baseline watt usage.

For example, if you plan to use a 10-amp device for 20 hours, you will need a battery with an RC of at least 200 amp-hours.

If you are using lead-acid batteries, you will need to double the battery rating to meet your energy needs, as discharging below 50% will rapidly damage the battery. Lithium-ion batteries, on the other hand, can be drained below 50% without suffering damage.

Cold-cranking amps

The CCA rating informs you of the number of amps required to ensure that cold weather does not hinder your engine's ability to start. It specifies the amps produced by a charged battery over a 30-second period while maintaining at least 7.2 volts at a temperature of 0°F (-18°C). This information is vital for batteries that need to be started frequently in frigid conditions, as cold temperatures cause batteries to operate less efficiently and slow down their reaction times.

To determine how many CCAs you need, a general guideline is to allocate about one amp for every cubic inch of engine displacement. Most boats will require between 250 and 600 CCA, depending on the size of their engines. However, it is always recommended to have a slightly higher CCA rating than you think you need to avoid any issues with starting your engine in cold weather.

CCA is different from Marine Cranking Amps (MCA), which are used to measure the amps produced at 32°F, the freezing temperature for water. MCA is relevant for water-based activities on boats, such as fishing and sailing. The distinction between MCA and CCA is that boats typically won't operate in water temperatures below 32°F. It's worth noting that MCA amps are generally higher than CCA because batteries can produce more current at 32°F compared to 0°F.

While most lithium batteries don't rely on CCA ratings, some, like the RELiON HP Series lithium battery, serve a dual purpose. They can provide the power needed to start the motor while also acting as a source of power for the trolling motor and electronics on a marine vehicle.

In summary, cold-cranking amps are a critical factor to consider when choosing a boat battery, especially in cold climates. CCA ratings help you understand the power needed to start your engine in cold temperatures and ensure optimal battery performance during harsh weather conditions.

Frequently asked questions