Boat Batteries: Self-Recharging Or Manual?

Boaters often wonder whether their boat batteries recharge themselves, and the answer is that it depends on the type of boat and battery. Most modern outboard motors with electric start functionality have an alternator that recharges the starting battery when the motor is running. However, this alternator does not charge the deep cycle batteries that power accessories like trolling motors, fish finders, and live well pumps. To recharge these batteries, boaters need a separate charger. This can be a portable charger, which is less expensive and can be used anywhere, or an onboard charger, which is mounted on the boat and can charge multiple batteries simultaneously. Onboard chargers are more convenient, as they only need to be plugged into a standard outlet to charge, but they are also more expensive.

Outboard engines and recharging

Outboard engines can be used to recharge a boat's battery, but this depends on the type of engine and battery setup. Most electric start outboard motors will recharge the battery as the boat runs, but it's a good idea to check your voltage before and after running the engine to ensure it's working. If your outboard engine doesn't recharge your battery, you can look into installing a rectifier/regulator and wiring harness to enable recharging. This setup involves connecting the rectifier/regulator to the engine and battery, and ensuring the wiring is properly fused and protected from the elements.

If you're considering adding recharging functionality to your outboard engine, it's important to consult a professional or a guide specific to your engine and battery setup. The process can be complex and may require additional components, such as a rectifier/regulator, wiring harness, fuses, and voltage meter. It's also crucial to understand your current electrical system and ensure any new components are properly integrated.

For those with electric start outboard motors, recharging the battery while the boat is running is a standard feature. However, it's always a good idea to carry a spare battery or a power pack as a backup in case of unexpected battery drainage. Additionally, regularly monitoring your battery's voltage and keeping it charged before trips can help ensure you don't run into issues while out on the water.

When preparing for a long trip without shore power, it's essential to consider how you'll keep your batteries charged. In addition to recharging through the outboard engine, options like solar panels, onboard charging systems, and portable generators can be utilised. Each of these methods has its own set of advantages and considerations, so it's worth researching which one best suits your boat and typical usage patterns.

Charging systems

One common approach is to utilise onboard charging systems. These systems can charge multiple batteries from a single plug outlet, making them convenient and efficient. This type of system is often used by professionals who require reliable and consistent charging solutions. Additionally, some onboard charging systems can be plugged into AC power outlets, providing flexibility during travel or when staying at motels with power availability.

Another option is to use portable generators to charge boat batteries. This is particularly useful when power outlets are not readily available. Solar chargers are also a viable solution, especially in areas with abundant sunlight. Solar chargers are environmentally friendly and can be used in remote locations, although their effectiveness may be limited by weather conditions such as rain, snow, or clouds.

Certain charging systems can also be used in conjunction with the boat's engine. These systems harness the power generated by the engine's alternator to charge the batteries while the boat is in motion. This dual-purpose approach not only charges the batteries but also powers other electrical components on the boat.

Additionally, there are various aftermarket charging solutions available, such as the StaynCharge and Stealth systems. These systems offer unique features like the ability to charge batteries while towing the boat or running the engine. They may include specialised wiring harnesses, smart boxes, and voltage sensing capabilities to optimise charging and extend battery life.

Overall, boat owners have a variety of charging systems to choose from, each with its own advantages and considerations. By selecting the most suitable system for their needs, boat owners can ensure that their batteries are adequately charged and maintained, providing uninterrupted power for their marine adventures.

Battery maintenance

Marine batteries are specifically designed for the extremes of long days of use with trolling motors and outboards. While automotive batteries are sometimes used to save money, they won't hold up as long under the heavy draw of a trolling motor.

• Always use marine batteries, with a cranking or starting type for the outboard and deep cycle for the trolling motor. Deep-cycle batteries can be discharged and recharged multiple times without damage and provide a steady power supply for longer.
• Check the electrolyte or water level in the battery before each charge and keep it filled to the manufacturer's recommendations. Do not overfill.
• Charge the batteries as soon as possible after use. The longer a battery stays discharged, the shorter its life will be.
• If your battery doesn't have a connector, clean the terminals every three months.
• Check all connections for tightness.
• Inspect the connections and terminals regularly for any corrosion. Keep the battery clean and free of dust or debris.
• When storing your boat for long periods, turn off the battery master switch and disconnect the batteries. Store them in a cool, dry place.
• Avoid overcharging the battery and using all of its charges regularly, as this will harm its life and performance.
• Keep the area around the battery ventilated during charging.
• Wear gloves when working around batteries to protect your hands from acid.
• Stick to one type of battery, as recommended by the boat dealer. Using different types can lead to underperformance and shorten the battery's lifespan.

Battery types

Marine batteries can be broadly categorized into three types: flooded lead-acid batteries, absorbed glass mat (AGM) batteries, and lithium-ion batteries.

Flooded Lead-Acid Batteries

Flooded lead-acid batteries are the oldest and most affordable type of marine battery. They consist of lead plates submerged in a mixture of distilled water and sulphuric acid. These batteries typically last 2-3 years with proper maintenance and are suitable for many boaters. However, they are bulky and heavy, weighing around 80 lbs each. They also require frequent maintenance, such as adding water, and are the slowest to charge.

Absorbed Glass Mat (AGM) Batteries

AGM batteries are an upgraded version of lead-acid batteries. They are maintenance-free and have a lower self-discharge rate, eliminating the risk of spilling harmful chemicals. While they are heavier and more expensive than lead-acid batteries, their benefits make them a popular choice among boaters.

Lithium-ion Batteries

Lithium-ion batteries are the newest addition to the market, offering several advantages. They are lightweight, about half the weight of lead-acid or AGM batteries, and have a longer lifespan, lasting up to 10-12 years. They provide a consistent discharge rate and can be discharged past 50% without damage. Although they have a higher upfront cost, their cost per year is comparable to other battery types over their lifespan.

Deep Cycle vs. Cranking Batteries

When selecting a marine battery, it's important to consider its purpose. Deep cycle batteries are designed for slow discharge over an extended period, making them ideal for powering trolling motors, fish finders, and other onboard electronics. On the other hand, cranking or starting batteries deliver short and strong bursts of power, perfect for starting your boat's engine.

Charging times

The charging time for a boat battery depends on several factors, including the type of battery, the charger used, and the charging conditions. Here is a detailed overview of the factors affecting the charging time of boat batteries:

Battery Type

Boat batteries typically fall into two categories: starting batteries and deep-cycle batteries. Starting batteries are designed to provide a quick burst of power to turn over the engine, while deep-cycle batteries are used to power accessories like trolling motors, fish finders, and live well pumps. The charging time can vary between these two types.

Charger Type and Compatibility

The choice of battery charger also significantly impacts charging time. Chargers can be portable or onboard, and they are designed for specific battery chemistries and voltages. It is important to match the charger to the battery's requirements for optimal charging.

For example, a 75Ah battery using a 7.5-amp charger will take approximately 10 hours to fully charge. Using a charger specifically designed for a particular type of battery can also reduce charging time.

Charging Conditions

The charging temperature can affect the speed of charging. Ionic lithium batteries, for instance, charge optimally above freezing temperatures, but they can be charged at temperatures as low as -4°F to -131°F without causing damage.

Battery Maintenance

Well-maintained batteries tend to charge more efficiently. It is recommended to clean the battery terminals before charging to ensure a smooth and efficient charging process.

Charging Process

The charging process itself involves several steps, including connecting the charger, monitoring the charging progress, and disconnecting the charger once the battery is fully charged. Smart chargers can automate some of these steps, but manual chargers may require more attention and time.

In summary, the charging time for a boat battery can vary depending on the type of battery, the charger used, the charging conditions, and the maintenance of the battery. By selecting the appropriate charger, maintaining the battery properly, and following the correct charging procedures, boat owners can ensure their batteries charge efficiently and effectively.

Frequently asked questions