Boat Battery Power: What Electricals Can You Run?

Onboard electrics are designed to make boating safer and more enjoyable. However, with the plethora of electronic gadgets available, keeping them all working can be a challenge. A boat's electrical system is usually categorised into two power systems: 12V DC low voltage for essential systems and a 230V mains system for luxury systems. The humble 12V battery is the source of all power for boats that are not plugged into shore power. This battery is charged by the engine's alternator or auxiliary battery charger. The battery's capacity is measured in amp hours, which indicates how many amps it can deliver over one hour. For example, a 110Ah battery can deliver 110 amps over one hour. However, it is important to note that the usable range of a battery is not the full range of its voltage. A fully charged battery will sit at around 12.6 volts, but the usable voltage drops to about 11.5 volts.

There are different types of batteries available for boats, each with its own advantages and disadvantages. Lead-acid batteries are the most common and affordable option, but they require regular maintenance and are larger and heavier relative to their power output. AGM batteries are high-performance, low-maintenance, and adaptable to a wide range of temperatures. Lithium-ion batteries offer higher energy density, providing more power in a smaller, lighter package, but they are more expensive.

Overall, the type of battery and electrical system a boatowner chooses will depend on their budget, power requirements, and how they intend to use their boat.

Starter vs. Leisure Batteries

Boats usually have two batteries or banks of batteries. One is for starting the engine, and the other is for running the domestic systems.

Starter Batteries

Marine starter batteries are designed to deliver high cold cranking amps (CCA) ratings and quick starting power. They are ideal for boaters who demand reliable performance every time they set sail. With their sturdy construction, low maintenance requirements, and long-lasting power, marine starter batteries are a great choice for powering marine adventures.

Leisure Batteries

Leisure batteries, also known as 'domestic' or 'house' batteries, are designed to provide small DC (direct current) voltages over a longer period. They have slightly thicker lead plates than ordinary cranking batteries, allowing them to withstand deeper discharges and tolerate being run flat. However, they require maintenance by topping up the cells with deionized water. They will also spill acid if tipped over and must be vented to avoid explosion if overcharged.

AGM Batteries

Absorbed Glass Mat (AGM) batteries are another option for both starter and leisure batteries. They avoid leakage by containing the acid within glass fibre mats between the plates. AGM batteries can accept high charging voltages and many charging cycles, making them suitable for high-current applications and maintenance-free.

Spiral Cell Batteries

Spiral cell batteries are similar to AGM batteries in that they use glass fibre mats to contain the acid. However, they have larger, thinner lead plates that are wound in a spiral. This design allows them to accept higher charge rates and tolerate more shaking and vibration.

Lithium-Ion Batteries

Lithium-ion batteries are the latest development in high-capacity battery technology. They offer a viable alternative to traditional lead-acid batteries, providing three times the power for three times the price. They are also significantly lighter, weighing about a third of an equivalent lead-acid battery. However, charging lithium-ion batteries requires close control.

Charging Batteries

Charging a boat battery is an essential skill for all boaters. It is important to note that boat batteries are different from car batteries as they are responsible for additional power needs such as lights, gauges, pumps, and other electronics on board. The process of charging a boat battery can be summarised in five simple steps:

• Choose the Right Charger: There are various types of boat batteries available in the market, and it is important to select a charger that matches your battery's chemistry and voltage. If you have multiple batteries on board, ensure the charger can accommodate all of them.
• Select the Right Time: The optimal charging temperature for ionic lithium batteries is above freezing, but they can be charged at temperatures as low as -4°F to -131°F without causing damage.
• Clean the Battery Terminals: Dirty battery terminals can disrupt the charging process, so it is important to clean them before connecting the charger.
• Connect the Battery Charger: Connect the charger by attaching the red (positive) cable to the red terminal and the black (negative) cable to the black terminal. Then, plug in the charger and turn it on.
• Disconnect the Charger: Once the battery is fully charged, disconnect the charger by first unplugging it, then removing the black cable followed by the red cable.

Additional Tips:

• Charging Time: A marine battery typically takes about four to six hours to charge from 0% to 80%.
• Battery Maintenance: Keep your battery fully charged to avoid issues like sulfation, which occurs when the battery remains partially charged for extended periods.
• Battery Storage: If your boat is not in use for a long period, use a battery maintainer or trickle charger to keep the battery healthy.
• Compatibility: Ensure your charger's voltage matches your battery's voltage, and the charger's amperage output is around 10-20% of the battery's capacity.

Different Types of Chargers:

Onboard Chargers: These are permanently installed on the boat and connected directly to the electrical system. They offer automatic charging by monitoring the battery's condition and adjusting the charging rate. Onboard chargers are ideal if you frequently use your boat near shore power sources or marinas.

Portable Chargers: These chargers are compact and versatile, designed to be carried on board or used on land. They are suitable for various battery types and are preferred when flexibility and mobility are crucial, such as when boating far from shore power.

Multistage Charging:

Smart chargers, available in both onboard and portable options, employ a multistage charging approach. This method includes bulk, absorption, and float stages, optimising the charging process and prolonging battery life. It prevents overcharging by gradually reducing the charging current as the battery nears full capacity.

AGM vs Lithium Batteries:

Deep cycle AGM (Absorbed Glass Mat) batteries require a specific multi-stage charging process to ensure optimal performance and longevity. Lithium marine batteries, on the other hand, have a different charging profile with built-in battery management systems to prevent overcharging and overheating. They offer faster charging times and can handle higher charge and discharge rates.

Prolonging Battery Life:

• Always keep your battery fully charged.
• Avoid letting the battery remain at a partial charge for extended periods.
• The less you deeply discharge the battery, the more cycles it will last.
• Do not overcharge the battery, especially during float charging, to prevent the disassociation of water in the electrolyte into hydrogen and oxygen.

By following these steps and tips, you can effectively charge and maintain your boat batteries, ensuring a reliable power source for all your boating adventures.

Battery Monitoring

• Understanding Battery Types: Different types of batteries have distinct characteristics. The two main types commonly found in boats are starting batteries and deep cycle batteries. Starting batteries provide short bursts of high current to turn the engine starter motor. On the other hand, deep cycle batteries are designed for small DC voltages over extended periods and can withstand deeper discharges.
• Battery Capacity and Discharge Rates: Battery capacity is measured in amp-hours (Ah) and indicates the available current a battery can deliver over a specified period. It's important to note that the faster you discharge a battery, the lower its capacity. Therefore, it's crucial to match the battery capacity to your current requirements to avoid long and frequent charge times.
• Battery Monitoring Products: There are various battery monitoring products available on the market. These include the Xantrex LinkLITE Battery Monitor, Victron BMV-712 Smart Battery Monitor, Victron SmartShunt 500A Bluetooth Battery Monitor, and Victron BMV-700 Battery Monitor, among others. These monitors provide real-time data and help you manage your battery power efficiently.
• Benefits of Battery Monitoring: By using a battery monitor, you can extend the life of your batteries and save money in the long run. Understanding how deeply you discharge your batteries is crucial, as it directly impacts the number of battery cycles you can expect. A battery monitor helps you avoid complete discharge, which can ruin your batteries, and guides you in optimising your battery power usage.
• Voltage Readings and Control Panel: It's not uncommon to observe different voltage readings between your battery monitor and control panel. This can be due to various factors, including the presence of surface charge on the battery plates immediately after charging. To address this, apply a load of 15 to 20 watts for ten minutes to stabilise the voltage.
• Battery Bank Management: Properly managing your battery bank is essential. This involves evaluating both the demand side (how much energy your electrical systems require) and the supply side (how you generate and store enough energy to meet that demand). Striking a balance between energy in and energy out is crucial to avoid disappointment and ensure your batteries are adequately charged and utilised.

Battery Maintenance

Correctly wiring your boat is essential. Batteries are the primary part of a vessel’s electrical system, so it's crucial to look after your marine battery. Here are some tips to optimise your boat battery's performance and longevity:

• Charge and discharge the boat's battery properly. Avoid overcharging as this can affect the lifespan.
• When not in use, store the battery in a cool, dry place to maintain its condition for extended periods.
• Inspect the connections and terminals regularly to identify any corrosion. Keep the battery clean and free of any dust or debris.
• Always wear gloves when working around batteries to protect your hands from acid.
• Stick to one type of battery once the boat dealer recommends it. Using different types of batteries can lead to underperformance of your boat electronics and shorten the lifespan of the battery bank.
• Turn off the battery master switch when you leave the vessel. When not in use for an extended period, disconnect the batteries.
• Check the electrolyte or water level in the battery before each charge and keep it filled to the manufacturer's recommendations. Do not overfill.
• Gases from batteries are highly explosive, so keep flames, sparks, and cigarettes away while filling or working around the battery.
• Always charge the batteries as soon as possible after use. The longer the battery stays discharged, the shorter its lifespan will be.
• If you don't have a specialised connector, the battery manufacturers recommend cleaning the terminals every three months.
• Check all connections for tightness.
• If you have a standard maintenance-type battery, check the electrolyte level. Top it up with distilled water and fully charge it before putting it away for an extended period.
• Disconnect the battery when storing it to prevent parasitic loads from drawing it down.
• Keep the battery in a warm area and use a battery maintainer to keep it fully charged.
• If your boat has a starting battery and a house battery, use a marine-grade main battery disconnect switch to turn everything off at once.

Battery Safety

Batteries are an essential part of a boat's electrical system, but they require careful handling to ensure safety. Here are some key considerations for battery safety on boats:

Ventilation and Secure Storage:

Ensure that batteries are stored securely in a well-ventilated area. The production of hydrogen, a highly flammable gas, is a by-product of battery charging. Proper ventilation helps minimise the risk of fire or explosion.

Battery Type and Maintenance:

Lead-acid batteries, commonly found on boats, require maintenance. Regularly top up the cells with deionized water and check for any spills or leaks.

Overcharging and Ventilation:

Overcharging lead-acid batteries can lead to the production of oxygen and hydrogen gas, which must be vented to avoid explosion.

Circuit Protection:

Proper circuit protection is crucial. Ensure every non-engine wire has circuit protection with a fuse or circuit breaker. This helps prevent excessive current flow, reducing the risk of overheating and fires.

Bilge Pump Bypass:

It is standard practice to bypass the main battery switch for the bilge pump. This way, even if the main switch is off, the bilge pump will activate if the boat starts filling with water.

Proper Wiring and Connections:

Use marine-grade wiring and connections. Ensure positive and negative wires are correctly identified and connected. Follow colour coding conventions for positive (red) and negative (black or yellow) wires.

Voltage and Current Awareness:

Understand the voltage and current capabilities of your batteries. Avoid exceeding their limits to prevent overheating and potential fires.

Emergency Preparedness:

Know how to cope without electrical power. Keep essential equipment, such as radios and navigation lights, operational through alternative power sources or manual operation.

Qualified Assistance:

For complex electrical systems or if you're unsure, seek assistance from a qualified marine electrician. They can help ensure your boat's electrical system is safe and properly installed.

By following these guidelines, you can enhance the safety of your boat's electrical system, particularly regarding battery usage and maintenance.

Frequently asked questions