Charging Boat Batteries: Using A Switch To Power Up

Charging boat batteries with a switch is a convenient way to manage your vessel's electrical systems. A marine battery switch allows you to control the flow of power between multiple batteries, providing the option to use or charge them individually or simultaneously. This is particularly useful when you have different types of batteries on board, such as starting batteries for the engine and deep cycle batteries for accessories. By isolating the starting battery, you ensure that you can always start your engine, even if the house bank is drained.

Charging multiple batteries simultaneously

If you have a dual bank battery charger, you can charge both batteries at the same time. This can be done by connecting the charger to the hot sides of the battery switch. This way, any time you have it plugged in, you are charging both batteries, and charging them separately.

Another option is to use a dual circuit plus battery switch (OFF-ON-COMBINE). This type of switch isolates the engine battery from the house bank. When the switch is turned to ON, the engine battery is connected to the engine and the house bank is connected to the house loads. The engine battery and house bank are completely separated so that all loads are connected to their respective batteries only. When the switch is turned to COMBINE, the alternators will charge both the engine and the house batteries.

A third option is to use a battery combiner such as a Blue Sea ACR (Automatic Charge Relay). This is a solenoid that connects the batteries together when they are being charged and separates them when they are being discharged.

Finally, if you are using shore power or a generator, the battery switch position does not matter. The charger should go straight to each bank.

Using a dual battery switch

Step 1: Understand Your Battery Switch

Before you begin, it's important to familiarise yourself with your boat's battery switch. The most common type is the OFF-1-2-BOTH switch, which allows you to select between battery 1, battery 2, or both. There are also dual circuit switches, which have an OFF-ON-COMBINE configuration and are designed to isolate the engine battery from the house bank.

Step 2: Install a Second Battery

If your boat currently has only one battery, it's a good idea to install a second one. This will give you backup power and peace of mind. Make sure the second battery meets your engine's specifications and complies with Coast Guard and ABYC standards. Secure the battery in a box or with tie-downs, and ensure the positive terminals are covered.

Step 3: Choose a Location for the Battery Switch

The battery switch should be installed as close to the batteries as possible, while also being easily accessible. Consider a location that is protected from spray, and leave enough space for the switch, which typically has a four- to six-inch-wide footprint. You can also opt for a flush-mount installation for a cleaner look.

Step 4: Connect the Positive Cables

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. Use marine-grade cables and cable lugs, and ensure all connections are secure and insulated with heat-shrink tubing.

Step 5: Connect the Negative Cables

For the dual-battery system to function correctly, you need a crossover cable between the negative terminals of the two batteries. Connect the negative cable lug from the engine/ground and the negative accessory wire to either of the negative battery posts. Again, ensure all connections are tight and properly insulated.

Step 6: Operating the Battery Switch

When charging your batteries, you can select the "BOTH" position on the switch to charge both batteries simultaneously. However, this is not recommended for extended periods as it can lead to overcharging. Instead, alternate between battery 1 and battery 2 to ensure each one gets charged adequately. When starting your engine, you can use the "BOTH" position in case of emergencies, but for regular operation, stick to using one battery at a time.

Avoiding common mistakes

Charging boat batteries with a switch requires careful attention to avoid costly mistakes. Here are some common mistakes to avoid when charging boat batteries with a switch:

• Using the wrong charger — It is important to use a charger that is compatible with your lithium battery. Using a lead-acid charger with a lithium battery can be risky and may damage the battery. Always check the manual before purchasing a charger to ensure it is suitable for your battery type.
• Charger with the wrong voltage/amps — Ensure that the charger's voltage and amps are compatible with your battery. The amp-hour (Ah) rating of the charger should not be higher than the Ah rating of the lithium battery.
• Not sufficiently discharging the battery — Lithium batteries should be discharged and recharged adequately. Aim to discharge the battery to 50-80% of its capacity before recharging. Partial discharges of only 10-15% can be detrimental to the battery's health.
• Not charging the battery long enough — Lithium batteries require different charging times depending on the charger and system used. To determine the ideal charging time, divide the amp-hours of the charger by the amps of the battery unit.
• Inadequate charging conditions — Although lithium batteries are more durable than lead-acid batteries, they should still be charged in a climate-controlled environment. Avoid charging in extremely hot or cold conditions to ensure the safety of your battery.
• Over-fusing of small DC-motor circuits — This occurs when a fuse with a higher amperage rating than recommended is installed. In the event of a jammed pump, if the fuse is rated too high, it may not trip and open the circuit, leading to a potential fire hazard.
• Incorrect battery charger installation — When installing a new battery charger, it is crucial to follow the manufacturer's recommendations for calibration. Overcharging can reduce battery life and create a dangerous situation.
• Inverter/Charger installations — DIY inverter installations are often done incorrectly. One common fault is a missing ground connection to the metal case of battery chargers, which can lead to a dangerous short circuit. Always follow the manufacturer's installation instructions or hire a certified technician.
• Stacked terminal issue — Avoid stacking too many wiring terminals onto a single lug, as this can create excessive electrical resistance and generate heat. Use a longer terminal strip to avoid stacking connections on the battery post.
• Unprotected DC-positive terminals — Insulating boots should be used to protect DC-positive terminals from potential short circuits. Without proper protection, a short circuit to the engine block can cause sparks and potentially start a fire.

Charging lead-acid batteries

Understanding Lead-Acid Batteries:

Lead-acid batteries, with their century-long history, are the traditional choice for boats. They come in two main types: flooded and sealed (or valve-regulated lead-acid, VRLA). Flooded batteries have caps that allow for water replenishment, while sealed batteries are maintenance-free. Sealed batteries include gelled electrolyte (gel cells), absorbed glass mat (AGM), and carbon foam AGM variants, each with unique characteristics.

Charging Techniques:

Battery Switches:

Battery switches play a crucial role in managing the charging process. The most common type is the OFF-1-2-BOTH switch, which allows combining battery banks for charging. However, it does not provide separation between engine and house loads. An alternative is the Dual Circuit Plus switch (OFF-ON-COMBINE), which isolates the engine battery from the house bank, ensuring that engine batteries are only used for starting and running the engine.

Charging with a Switch:

When charging lead-acid boat batteries using a switch, follow these steps:

• Understand your battery type: Know whether you have AGM or Gel Cell batteries, as this affects the charging approach.
• Choose the right charger: Select a charger suitable for your battery type and charging needs. A 10-amp to 20-amp charger is typically recommended. Smart chargers with multiple stages are ideal for preventing overcharging.
• Connect the charger: Attach the charger clips to the corresponding terminals on the battery. Smart chargers will provide feedback on the battery's status.
• Initiate charging: Start the charging process and wait until it is complete. Charging times vary depending on the battery's charge level and the charger's capacity.
• Reinstall the battery: Once charging is complete, securely reinstall the battery, ensuring all connections are tight but not overtightened.
• Maintain battery health: Regularly check your battery's charge level and perform maintenance, such as cleaning corroded terminals, to extend its service life.

Additional Tips:

• Always charge in a cool, well-ventilated area.
• Turn off the engine ignition before disconnecting the battery.
• Don't mix battery brands and types if you have a battery bank.
• Store batteries in a cool, dry place during the off-season.

Maintaining deep cycle batteries

Keep Batteries Charged:

Lead-acid batteries should be charged as soon as possible to prevent sulfation, which renders the battery incapable of holding a charge. Lithium-ion batteries are less susceptible to partial charges, but it's still best to keep them charged.

Avoid Extreme Temperatures:

High temperatures significantly reduce battery lifespan, with every 15 °F above 77 °F halving the expected life. Cold temperatures also affect performance, decreasing capacity and requiring more current to charge.

Avoid Inactivity:

Batteries prefer to be used rather than stored. If storing is necessary, charge the battery, disconnect all cables, and store it in a cool place, boosting the charge every two months.

Avoid Deep Discharge:

Regularly discharging lead-acid batteries beyond 50% will reduce their lifespan. Lithium-ion batteries have a higher depth of discharge (80-90%), but full discharge should be avoided for all battery types.

Maintain Water Levels:

Flooded lead-acid batteries require distilled or deionized water to be added every two weeks, ensuring the plates are covered but not overfilled.

Perform Equalization:

Equalization, a low-current extended charge, helps balance the cells in your battery and should be done every 1-3 months for both lead-acid and lithium-ion batteries.

Keep Batteries Clean:

Remove dust and debris from batteries to prevent current leakage.

Use a Charge Controller:

A charge controller is essential for safety when using batteries in a solar panel system, protecting against overvoltage and preventing partial-charge use.

Inspect and Clean Connections:

Regularly inspect connections to ensure they are tight and secure, and clean any corrosion with a baking soda and distilled water paste.

Consider Lithium-ion:

Lithium-ion batteries are lighter, more efficient, require less maintenance, and have a higher depth of discharge. They are a more modern and reliable option than lead-acid batteries.

Frequently asked questions