Boat Batteries: Powering Your Craft, Doubling Your Fun

Adding a second battery to a boat is a simple project that can give you peace of mind. It's a good idea if you want to add powerful accessories like a stereo subwoofer system, cabin lighting, or an electric windlass. The most basic setup involves a dual battery switch, which lets you choose one of the two batteries, combine them, or disconnect both with the turn of a dial. More complex systems automatically charge both batteries regardless of the switch position. When installing a second battery, it's important to follow safety standards and choose the right type of battery for your boat's engine and electrical system.

The simplest setup involves a battery switch, which lets you choose one of the two batteries, combine them, or disconnect both

The simplest setup for a dual battery system involves a battery switch, which lets you choose one of the two batteries, combine them, or disconnect both. This setup is straightforward to install and provides peace of mind in case of a dead battery. It is also upgradeable and can be made more complex by incorporating automatic charging features.

To begin the installation, you will need a second marine battery that meets your engine specifications. It is important to ensure that the batteries are secured properly, following Coast Guard and American Boat and Yacht Council (ABYC) standards. Wet-cell batteries should be placed in a battery box, while absorbed glass mat batteries do not require one. Both types need tie-downs or brackets, and it is recommended to cover the positive terminals with non-conductive boots.

Next, select a location for the battery switch that is easily accessible and complies with ABYC standards. The switch should be installed as close to the batteries as possible, and you may want to consider flush-mounting it for a neater appearance. However, ensure that it is protected from spray.

Now, you can start connecting the cables. First, connect the positive terminals of both batteries to the corresponding posts on the back of the switch. Then, connect the positive cable from the engine to the output post of the switch, along with the positive accessory wire. It is important to note that you should use cables stamped with "marine cable" on the insulation and sized appropriately for your engine.

Finally, connect the negative cables. This includes a crossover cable between the negative terminals of the two batteries, as well as the negative cable lug from the engine/ground and the negative accessory wire to either of the negative battery posts. Ensure that all terminal nuts are tightened securely.

With this setup, you can now choose to use one battery at a time, combine them, or disconnect both. Remember to never switch the batteries while the motor is running. This simple dual battery system provides flexibility and peace of mind for boat owners.

A more complex system has automatic charging, regardless of the switch position

A more complex system that offers automatic charging, regardless of the switch position, is a dual-circuit system. This system combines a Dual Circuit Plus switch with an Automatic Charging Relay (ACR). This setup provides greater flexibility and control over the boat's electrical system.

The Dual Circuit Plus switch allows for the isolation of the Start and House circuits, preventing accidental discharge of both batteries. When in the ON position, it keeps the batteries separated, ensuring that only one battery is in use at a time. This feature helps to prevent a situation where both batteries are fully discharged.

The ACR, also known as a Voltage Sensitive Relay, is a crucial component of this system. It automatically manages the dual circuit switch positions, ensuring your batteries are charged and ready without any manual intervention. The ACR senses when a charging source is applied to either battery and closes the circuit accordingly. When the charging source is removed, the ACR opens the circuit after a short time delay to prevent temporary voltage sags.

This automatic charging system offers several advantages. Firstly, it eliminates the hassle and worry associated with manual battery management, providing a hassle-free boating experience. Secondly, it can handle high amp loads, making it suitable for use with devices like trolling motors or windlasses. Lastly, it provides passive control over the battery system when combined with an ACR, simplifying the operation and removing the need to manually switch between battery banks.

The ON-OFF-COMBINE switch is another option for boaters seeking a more advanced battery management solution. This switch offers greater control and flexibility, allowing the user to choose which battery to use and when. It provides the ability to isolate a battery in emergency situations, preventing potential damage or safety hazards. However, it is important to note that this switch may require additional wiring or installation steps due to its complexity.

In summary, a dual-circuit system with a Dual Circuit Plus switch and an ACR provides automatic charging, ensuring your batteries are always ready for use. This system offers increased flexibility, improved safety, and simplified operation, making it a convenient choice for managing your boat's electrical system.

The dual-purpose battery is a good compromise between starting and deep-cycle batteries

Marine batteries are essential for boats, and there are different types available, each with its own advantages and disadvantages. Starting batteries, for instance, are similar to automotive batteries and can supply a lot of current for a short period of time. However, they need to be recharged almost immediately and are not tolerant of deep discharges. On the other hand, deep-cycle batteries can endure repeated deep discharging and recharging without damage and are available in flooded and sealed battery types.

While both starting and deep-cycle batteries have their benefits, a dual-purpose battery offers a good compromise between the two. Also known as sealed dual-purpose batteries, they combine the ability to withstand deep discharges with cranking power to start an engine. This makes them ideal for boats with two identical batteries used interchangeably for starting and house electrical loads.

One of the main advantages of dual-purpose batteries is their ability to tolerate deep discharges that would typically ruin a starting battery. This is especially useful for boats with minimal DC loads where the engine is always running, such as wakeboard boats, runabouts, and personal watercraft. Additionally, they are available in both flooded and sealed battery types, offering flexibility in terms of installation and usage.

However, it is important to note that dual-purpose batteries have lower storage capacity than comparably-sized deep cycles. As such, they are best suited for boats with two identical batteries, allowing for easy interchangeability between starting and house electrical loads. By installing a dual-purpose battery, boat owners can benefit from the advantages of both starting and deep-cycle batteries, without having to worry about frequent recharging or deep discharges.

A second battery can be added in parallel to the existing one, increasing capacity while maintaining the same voltage

To set up a parallel connection, you'll need to connect the positive terminal of the new battery to the positive terminal of the existing battery, and similarly, connect the negative terminals of both batteries together. This will give you a longer-lasting power supply while keeping the voltage the same.

It is important to ensure that the batteries you are connecting in parallel are of the same type and have similar characteristics, such as voltage and capacity. This is crucial for the proper functioning and longevity of your batteries.

Additionally, when connecting batteries in parallel, always exercise caution and adhere to safety guidelines. Batteries contain a significant amount of energy, and improper handling can lead to short circuits or electrocution. Always disconnect the positive battery cables from the terminals before working on the electrical system.

By adding a second battery in parallel, you can enhance the capacity of your boat's power supply, providing peace of mind and ensuring you have the power you need for your marine adventures.

An automatic charging relay (ACR) can be used to automate the charging process and isolate the starting battery from the accessories battery

An automatic charging relay (ACR) is a simple way to automate the charging process and manage a boat's multiple battery banks. It is a fully automatic, voltage-triggered switch that connects and disconnects batteries during the charging cycle to prevent overcharging and protect the starting battery from discharge.

The ACR combines the batteries when charging voltage is present and separates them when there is no charging voltage. This automation eliminates the need for manual intervention and reduces the risk of human error, such as forgetting to switch off the charger, leading to drained batteries.

The Blue Sea Systems ACR is one of the most popular charge management devices on the market today. It can be used with various charge sources, including alternators, solar panels, wind turbines, and AC chargers. The ACR is installed between the positive terminals of each battery bank, with fuses protecting the wires from the battery bank in case of a short circuit.

When choosing an ACR, it is important to consider the output rating of the alternator, the largest load on the auxiliary battery, and additional features such as auxiliary battery priority and start isolation. By installing an ACR, boat owners can effectively manage their battery charging and ensure that all batteries are adequately charged without the need for a dual-output charger, making it a cost-effective solution.

Frequently asked questions