Boat Battery: To Switch Off Or Not?

Owning a boat is a lot of fun, but it also comes with a lot of responsibility. One of the most important things to know about boat maintenance is how to properly care for your boat's battery. So, should you turn your boat battery off when you're not using it?

The answer depends on a few factors, such as the type of boat you have, how you store it, and the type of battery you have. If you store your boat on land, it's generally recommended to disconnect the battery to prevent it from draining. However, if you store your boat in the water, it's important to leave the battery on so that the bilge pumps have power and can remove any rising water inside the bilge.

It's also important to consider the type of battery you have. Lithium-ion and AGM (absorbent glass mat) batteries are more resistant to vibrations and can withstand tougher marine environments. On the other hand, car batteries are not designed for the harsh vibrations experienced in boats and should not be used as a substitute for marine batteries.

To maximise the lifespan of your boat battery, it's recommended to keep it charged when not in use and to store it in a cool, dry location during the off-season. Additionally, regular maintenance and cleaning of the battery terminals are crucial to ensuring your battery stays in good condition.

Disconnecting the battery when your boat is stored on land

If you are storing your boat on land, it is recommended to disconnect the battery to prevent it from draining. Even when your boat is turned off, your battery could still be drawing power from things such as the radio, bilge pump, fish finder, or even a clock. Over time, these items will slowly drain your battery, especially if the battery is wired directly to any of these objects.

If you plan on storing your boat for a few weeks, it is best to disconnect the battery and ensure it has a full charge. This will allow it to sit safely for several weeks without draining. If you have a wet-cell battery, you should also pop the cap on the top of the battery case and top up the level with distilled water.

• Start by removing the negative (black) cable. You may need a wrench or a set of pliers to loosen the nut.
• With your hand, twist and carefully pull up on the cable near the end and slowly slide it off the terminal.
• If the cable doesn't move, do not use a screwdriver to pry it off as this could cause damage. Instead, use a battery terminal puller, which is a cheap and useful tool for every boat owner.
• Once the negative cable is removed, tuck it off to the side and out of the way.
• Next, loosen and remove the positive (red) cable from the battery, again being careful not to pull too hard. Tuck the cable out of the way.

Now that your battery is disconnected, you can store it in a cool, dry place. It is recommended to store your boat battery indoors, such as in a basement or workshop, as marine batteries should not be left outside in the cold for extended periods. If you live in an area with extremely cold temperatures, your battery may freeze, which can cause damage.

During the winter months, it is especially important to properly maintain and store your boat battery. If you have a wet-cell battery, make sure to check the electrolyte level and top it up with distilled water as needed. For gel cell and absorbed glass mat (AGM) batteries, you don't need to worry about topping up the water, but you should periodically check that they still have a charge above 80%.

In addition to proper storage and maintenance, there are a few other things to keep in mind when disconnecting your boat battery:

• Before storing your battery, inspect it for any signs of damage, corrosion, or leaks. Clean the battery terminals with a mixture of baking soda and water to remove any dirt or corrosion.
• If you have a dirty battery, give it a wipe-down with a clean cloth. A dirty battery can discharge more quickly than a clean one.
• Every 4 to 6 weeks, check the health of your battery to ensure it is still holding a full charge.
• If you have a wet-cell battery, make sure the cap on the battery case is secure to prevent evaporation and maintain the proper water level.
• Do not store your boat battery directly on a concrete floor, as this can cause the battery to discharge more quickly.

Keeping the battery on to power the bilge pump

If you store your boat in the water, it is recommended to keep the battery on to power the bilge pump. This is because you want to make sure that the bilge pump has power in case the water level rises inside the bilge.

In this case, instead of disconnecting the battery, you could consider using a charger to ensure the battery remains fully charged. A four-stage "smart charger" with a built-in microprocessor to monitor the battery charge and automatically shut off when the battery is fully charged is ideal. This will prevent the battery from drying up and overheating, reducing the risk of fire.

If you have a wet-cell battery, it is important to periodically check the electrolyte level and top it up with distilled water. Additionally, ensure that the pump is securely fastened and the discharge fitting is placed above the waterline to prevent ocean water from siphoning back into the bilge.

It is also crucial to get the pump wiring out of the bilge as quickly as possible. Secure the wires to prevent them from sagging into the bilge water. Connect the bilge pump directly to the battery, not through the distribution panel, and fuse the positive side as close to the battery as possible.

By following these guidelines, you can effectively keep your boat battery on to power the bilge pump while mitigating the risks associated with a drained or faulty battery.

Using a solar panel to maintain the battery charge

When selecting a solar panel, it is important to consider the size of your boat, the capacity of your battery, and the amount of power you need to generate. For most boats, a single 100-watt solar panel is sufficient for maintaining a marine battery charge over a short period. However, larger boats or those with higher power demands may require multiple or larger panels. The efficiency of a solar panel is also a key factor, as it determines how much power it can generate from the available sunlight. Higher-efficiency panels can generate more power with fewer panels, which is beneficial given the limited space on boats.

To charge a marine battery using a solar panel, several components are necessary. Firstly, you will need a charge controller to regulate the charging process, prevent overcharging, and protect the battery from excessive discharge. Secondly, high-quality cables and connectors are needed to establish reliable connections between the solar panel, charge controller, and battery, ensuring efficient power transfer. Mounting hardware is also required to securely install the solar panel on the boat, maximising sunlight exposure and providing stability.

When installing the solar panel, it is important to choose a location on the boat that receives ample sunlight throughout the day, ensuring it is clear of obstructions that could cast shadows. Solar panels should be mounted horizontally, as they give maximum output when perpendicular to the sun's rays, and boat movement can make inclining the panel towards the sun unpredictable. Common locations include radar arches, T-tops, and biminis, but deck mounting is also effective as long as the chosen spot remains shadow-free when the sun is high.

Wiring the solar panel is a straightforward process, involving connecting the positive terminal to the positive battery post and the negative terminal to the negative battery post. Additionally, a fuse close to the battery is essential to prevent a potential fire in the event of a short circuit.

Solar panels offer a sustainable, efficient, and environmentally friendly solution for boat owners, allowing them to maintain their battery charge without relying on traditional power sources.

Using a multistage charger to preserve the battery's charge

Using a multistage charger is an effective way to preserve your boat battery's charge. These chargers are designed to optimise the charging process, ensuring that your marine batteries are charged efficiently and safely. Multistage chargers are also known as "smart chargers" and are available in both portable and onboard models. They are particularly useful if you store your boat on the water, as they can keep your bilge pumps working.

Smart chargers employ a multistage charging approach, typically involving bulk, absorption, and float stages. This method speeds up the charging process and safeguards the battery's longevity by preventing overcharging. Overcharging can cause significant damage to batteries and reduce their lifespan. By gradually reducing the charging current as the battery nears full capacity, smart chargers avoid this issue.

Onboard marine chargers are permanently installed on the boat and connected directly to its electrical system. They offer the advantage of automatic charging, continuously monitoring the battery's condition and adjusting the charging rate accordingly. These chargers are ideal if your boat is usually near shore power sources or marinas, eliminating the need for a portable charger.

Portable chargers, on the other hand, are compact and versatile. They can be carried on board or used on land to charge batteries when docked. They are a good option if you need to charge batteries on multiple boats or if your boat is too small to accommodate an onboard charger. However, they can be inconvenient to set up and are more susceptible to theft.

When choosing a multistage charger, it's important to consider the type and number of batteries on your boat. Determine whether you have wet-cell, gel, or AGM batteries, as they respond differently to charging methods. Additionally, consider the number of batteries and engines on your boat, as this will impact the configuration and output requirements of the charger.

It's also crucial to follow the manufacturer's instructions for charging and maintaining your specific battery type. By using a multistage charger and adhering to proper maintenance practices, you can extend the life of your boat battery and ensure reliable power during your boating adventures.

The dangers of overcharging a marine battery

Overcharging a marine battery can lead to several issues, from damaging the battery to causing a safety hazard. Here are some of the dangers of overcharging a marine battery:

Reduced Battery Life and Performance

Overcharging a marine battery can be harmful to the battery's lifespan and performance. It can cause the battery to degrade over time, reducing its ability to hold a charge. This means that the battery will need to be replaced more frequently, which can be costly.

Heat Generation and Thermal Runaway

The excess energy from overcharging can lead to heat generation within the battery cell. In some cases, this can result in a "thermal runaway" situation, where the temperature in the cell continues to rise exponentially, initiating chemical reactions that cannot be stopped. This can lead to the cell opening, possibly burning down, and releasing toxic gases.

Safety Risks

The heat generated from overcharging can pose a safety risk to the user. In the worst-case scenario, it could lead to a fire or explosion. Therefore, it is crucial to prevent overcharging to mitigate these risks.

Damage to Charging Sources

Charging sources, such as alternators, solar or wind chargers, can be permanently damaged if they are run at full capacity for too long to charge a less-than-fully-charged marine battery. While they may not be damaged immediately, their lifespan will be reduced, and they may fail prematurely.

Swelling of the Battery Cell

Overcharging can also lead to the severe swelling of the battery cell, especially in lithium-polymer batteries. This swelling can further increase the risk of thermal runaway and burnout.

Void Insurance

In some cases, leaving your marine battery charger on at a marina might void your boat insurance. It is essential to check with your insurance provider and marina management to understand their specific guidelines and requirements.

To avoid these dangers, it is crucial to use suitable chargers and charging profiles for your marine battery. Additionally, regularly monitoring and maintaining your battery can help ensure it remains in good condition and reduce the risk of overcharging.

Frequently asked questions