Choosing The Right Battery For Your 20-Foot Boat

Choosing the right battery for your boat is essential to ensure optimal performance and avoid damaging your boat's electrical system. The type of battery you need will depend on several factors, including the size of your boat, the power requirements of your engine and on-board electronics, and your budget.

There are three main types of marine batteries: starting (or cranking) batteries, deep-cycle batteries, and dual-purpose batteries. Starting batteries deliver short bursts of energy to start the engine, while deep-cycle batteries provide consistent power over a long period for electronics and appliances. Dual-purpose batteries combine the functions of both starting and deep-cycle batteries but are less efficient than specialised batteries.

When selecting a marine battery, you should also consider the battery chemistry, such as lead-acid (including flooded, AGM, and gel batteries) or lithium. Lead-acid batteries are more affordable but heavier and require more maintenance, while lithium batteries are lightweight, durable, and easy to maintain.

Additionally, factors like battery power, size, voltage, cold cranking amps (CCA), and reserve capacity should be considered to ensure the battery meets your boat's specific requirements.

Starting/Cranking Batteries

Starting batteries, also known as cranking batteries, are designed to deliver quick bursts of energy to start a boat's engine. They are not intended for extended, continuous use, as the alternator takes over once the engine is running. The purpose of a starting battery is to provide a separate power source to ensure that a dead battery doesn't leave you stranded.

Cranking amps (CA) is a measure of a battery's ability to deliver a burst of power at 32°F (0°C) for 30 seconds while maintaining a minimum voltage. CA is used to assess the battery's starting power in relatively mild or moderate climates.

Cold cranking amps (CCA) is a more stringent measure, defined as the maximum current a battery can deliver at 0°F (-18°C) for 30 seconds, and it is crucial for cold-weather starting. CCA and MCA (Marine Cranking Amps) indicate how well a battery can crank an engine in low-temperature conditions.

When choosing a starting battery, it's important to consider the size and power needs of your boat. Most boat owners will want somewhere between 300-500 CCAs for starting their boat, based on the engine's size. Remember that you can always use more amps, but not having enough will limit performance.

Starting batteries are typically designed for short bursts of high current and have a lifespan of around 3 to 5 years. They are essential for boating, as they provide the electrical energy needed to start the engine.

There are different types of starting batteries available, such as flooded lead-acid batteries, AGM (Absorbed Glass Mat) batteries, gel batteries, and lithium-ion batteries. Flooded lead-acid batteries are the most traditional and affordable, while lithium-ion batteries are the newest and most advanced, offering high energy density and a long lifespan.

When selecting a starting battery, consider factors such as your budget, boat size, engine type, and the usage of onboard electronics. Larger boats and high-performance engines may require higher-capacity starting batteries, while smaller boats may need lower-capacity ones.

Proper charging and maintenance are crucial for maintaining the performance and longevity of starting batteries. Use a compatible charger designed for marine batteries, and avoid overcharging or undercharging. Regularly check the battery terminals for corrosion and keep them clean.

Deep-Cycle Batteries

When choosing a deep-cycle battery, it is important to consider the battery's capacity and power output. The amp-hour (Ah) rating measures the battery's capacity and indicates how much energy can be stored. The higher the Ah rating, the longer the battery can provide power. For example, a 12v 125Ah battery can deliver 125 amps for an hour.

Another important consideration is the battery's cranking power, especially in cold temperatures. Cold-cranking amps (CCA) refer to the battery's ability to deliver amps in cold weather, while marine cranking amps (MCA) refer to its cranking power in the warmer marine environment. Most boaters should focus on MCA.

Dual-Purpose Batteries

When choosing a dual-purpose battery, it is important to consider the boat's size and power needs, as well as the type of battery. For example, a small boat with minimal electronics will have different power requirements than a large vessel with sophisticated systems. It is also crucial to check the cold cranking amps (CCA) and marine cranking amps (MCA) to ensure the battery can crank the engine in low-temperature conditions.

Some popular options for dual-purpose marine batteries include the Exide Edge Flat Plate AGM Sealed Marine Battery, which offers 775 CCA and 145 minutes of reserve capacity, and the Optima Starting & Deep Cycle Marine Battery, which provides 750 CCA and up to 120 minutes of reserve capacity.

It is worth noting that dual-purpose batteries have been known as "jacks of all crafts and masters of none". Some may not provide enough power to start specific motors, and regular deep-cycle batteries tend to have shorter lifespans than specialised alternatives. However, lithium dual-purpose batteries are an exception, offering both power and longevity.

Battery Chemistry

Marine batteries are available in three different chemistries: flooded lead acid, AGM (absorbed glass mat), and lithium iron phosphate (LiFePO4). Each type has its own advantages and disadvantages, and the right choice depends on factors such as budget, weight, maintenance requirements, and performance.

Flooded lead-acid batteries are the most traditional and affordable option. However, they are large and heavy, and require frequent maintenance, including regular topping up of the electrolyte with distilled or deionized water. They have the shortest lifespan among the three types and a high self-discharge rate.

AGM batteries, on the other hand, are sealed and require no additional maintenance. They have a longer lifespan than flooded lead-acid batteries and discharge slower during storage. AGM batteries are also more resistant to vibrations and extreme temperatures. However, their storage capacity is relatively small compared to their overall footprint.

Lithium iron phosphate batteries are a newer option, offering several advantages over the other two types. They are lightweight, durable, and quick to recharge. Lithium batteries have a high cycle life and a better depth of discharge than lead-acid batteries. They are also safe, secure, and maintenance-free. However, they come with a higher initial investment cost.

When choosing the right battery chemistry for a 20-foot boat, factors such as power requirements, budget, weight constraints, and desired performance should be considered. Lithium batteries, despite their higher cost, offer a lightweight, low-maintenance, and high-performance option ideal for boaters. AGM batteries, while having lower storage capacity, provide a good balance between cost and performance. Flooded lead-acid batteries, though affordable, require more maintenance and are heavier, which may impact the boat's speed and fuel consumption.

Battery Size

The size of the battery you need for your 20-foot boat depends on several factors, including the type of battery, the power requirements of your boat, and the chemistry of the battery.

Firstly, you need to determine whether you need a starting battery, a deep-cycle battery, or a dual-purpose battery. A starting battery provides short bursts of power to crank your boat's engine, similar to a car battery. A deep-cycle battery, on the other hand, delivers consistent power over a long period and is ideal for running electronics and appliances. Dual-purpose batteries combine the functions of both starting and deep-cycle batteries but are less efficient than specialised batteries.

To estimate your boat's power needs, you should make a list of all the electrical equipment on your boat, including lights, bilge pumps, trolling motors, and other gadgets. Then, determine the electric consumption and running time for each device, and calculate the Amp-hour rating by multiplying the ampere consumption and running duration. Add up the Amp-hour ratings of all the devices to find the total power draw, and consider adding a buffer of 20-30% to account for losses and higher electrical requirements. This will give you the Amp-hour rating that your battery should have.

Another factor to consider is battery chemistry. Flooded lead-acid batteries, AGM (Absorbed Glass Mat) batteries, gel batteries, and lithium batteries each have their own advantages and disadvantages in terms of weight, maintenance, discharge rate, and cost. For example, flooded lead-acid batteries are affordable but heavy and require frequent maintenance, while lithium batteries are lightweight, durable, and easy to maintain but come with a higher price tag.

The physical dimensions and weight of the battery are also important considerations, as you need to ensure it fits within your battery compartment and doesn't add excessive weight to your boat. Additionally, the voltage of the battery should match your boat's electrical system, typically 6V, 12V, or 24V.

Finally, the Cold Cranking Amps (CCA) rating is crucial, especially if you plan to operate your boat in cold conditions. The CCA indicates the battery's ability to crank the engine in low temperatures, and a higher CCA rating will provide better cold-starting performance.

Frequently asked questions