Replacing Boat Battery Chargers: A Step-By-Step Guide

Replacing a boat battery charger is a fairly simple task that can be completed in a few hours. It involves selecting an appropriate charger, finding a suitable location for it, and then mounting and connecting the charger.

When selecting a charger, it is important to choose a quality marine-grade unit that meets the appropriate standards and has the right output for your battery capacity. It should also be ignition-protected if your boat is gasoline-powered.

When choosing a location, it is best to pick a cool, dry area with good ventilation that is not too close to the batteries, as they produce corrosive gases while charging.

Once you have selected a location, you can mount the charger using screws or bolts, ensuring that the surface can support its weight. Then, you can connect the charger by routing and attaching the DC and AC leads, making sure to follow the correct polarity and using the correct tools to secure the connections.

Finally, you can test the charger by plugging it into a power source and checking the LED indicator panel to ensure it is functioning correctly.

Choosing the right charger

Battery Type

First, determine the type of battery you have. The most common types are AGM (absorbed glass mat), flooded or wet cell, Gel Cell, and VRLA (valve-regulated lead-acid). It's important to note that Gel Cell batteries require a specific type of charger, while most other battery types can use a standard charger.

Voltage

The voltage of the charger must match the output voltage of the battery. Most marine batteries are 6-volt or 12-volt, so you'll need a charger with a corresponding voltage. Using a charger with the wrong voltage can damage your battery and even cause a safety hazard.

Amp/Hour Capacity

Amp hours refer to how much charge can be stored in the battery. It's crucial to choose a charger that matches your battery's amp-hour capacity to avoid delivering too much or too little current. As a general rule of thumb, choose a charger with an output that's at least 10% of your battery's amp-hour capacity.

Temperature

The ambient temperature of the environment you'll be operating your boat in is an important consideration when choosing a charger. If you plan to operate your boat in high temperatures, you'll need a lower charging voltage. Conversely, if you'll be operating in temperatures below 40°F (4°C), you'll need a higher charging voltage.

Features

Look for a charger with features that match your specific needs. For example, some chargers offer specific charge modes for different battery types (lead-acid, gel, AGM). Others may offer temperature sensors, which are useful because a hot battery is less able to accept a charge than a cooler one. Smart chargers provide numerous charging options and can be a good choice.

Quality and Standards

It's important to choose a quality marine-grade charger that meets industry standards, such as those set by the American Boat and Yacht Council (ABYC) and UL. Avoid cheap automotive chargers, as they can cause problems such as overcharging and corrosion. A marine battery charger is designed to be connected permanently to the battery bank and will not harm the batteries even if left on for extended periods.

Location

When installing the charger, choose a location that is cool, dry, and well-ventilated. Higher locations are generally better as they provide better ventilation and protection from the corrosive humidity of the bilge. Avoid mounting the charger directly over the batteries, as the gases released during charging can damage the charger. Keep wire runs as short as possible and use the correct gauge to avoid voltage drop.

Selecting a location

Ventilation and Temperature:

• Choose a cool, dry area with adequate ventilation. Good ventilation is crucial to prevent the buildup of corrosive gases and humidity.
• Avoid mounting the charger directly above the batteries. Batteries, especially liquid electrolyte or "wet cell" types, release corrosive gases during charging, which can damage the charger if placed too close.
• Keep the charger away from high-temperature locations, such as the engine compartment, if possible.

Proximity to Batteries:

• Place the charger as close to the batteries as practical. Shorter cable lengths reduce installation costs, minimise voltage drop, and improve charger performance over its lifespan.
• However, do not compromise ventilation and safety by mounting the charger too close to the batteries.

Accessibility and Convenience:

• Select a location that allows for easy access to the charger's AC power cord. You may need to route the cord through a bulkhead or locker to keep it dry and accessible.
• Consider installing additional locker vents to increase airflow around the charger if ventilation is limited.

Weight and Mounting:

• Ensure the mounting surface can support the weight of the charger. Heavier chargers may require through-bolting, while smaller chargers can be mounted with screws.
• Use the supplied template to mark and drill mounting holes. Use marine-grade stainless steel fasteners to secure the charger in place.

Safety:

• Battery chargers installed on gasoline-powered vessels must be ignition-protected and conform to relevant UL specifications, including testing in an explosive environment.
• Avoid placing the charger in areas where it could be exposed to moisture or water spray, as this could pose a safety hazard.

Remember to follow the manufacturer's instructions and recommendations when selecting the location for your boat battery charger.

Mounting the charger

Now that you've picked a suitable spot to mount your charger, it's time to get it in place. For smaller chargers being mounted to a thick bulkhead or structure, screws are an acceptable option. If the charger weighs more than a couple of pounds, however, it should be through-bolted. Regardless, make sure you use marine-grade stainless steel for all mounting hardware.

Use the supplied template to mark and drill the mounting holes with a 1/8-inch bit. Then, use a screwdriver and the supplied mounting screws to attach the charger, bedding each screw with marine sealant.

It's important to keep the charger in a dry, well-ventilated location. Avoid mounting it directly above the batteries, as escaping gas can compromise the charger. Keep wire runs as short as possible and use the correct gauge to avoid voltage drop.

Additionally, keep the charger away from the compass. Mounting it closer than a couple of feet is likely to cause some compass deviation.

Connecting the wiring

The DC cables should be connected to the charger as directed by the manufacturer. If a wire-to-wire connection must be made, it should be done using a butt splice, preferably one with adhesive heat-shrink tubing and secured inside the wiring compartment on the charger. If the charger is a potted type and has cables embedded in it, do not extend the wires. If the DC wiring is terminated with alligator clips, they should be cut off and terminated with proper ring terminals to prevent the alligator clips from causing a spark, which could lead to a battery explosion.

When connecting the wires to the battery, put the charger wire on top of the big battery cables, not under them. Spray or coat the terminals with a corrosion preventative. Try to use closed barrel terminals and heat shrink or tape over the terminal. The most common wiring failure is corrosion caused by acid and gas wicking up the wire, leading to eventual failure. Sealing, corrosion preventatives, and routing wires so the terminals are away from the battery caps help forestall failures due to corrosion.

The AC wiring can be as simple as plugging the charger into an extension cord and running that to an outlet in your garage. For a more permanent installation, another option is to install a grounded AC power inlet that accepts a standard extension cord. If your boat already has an AC system installed, plugging the charger into a convenient outlet (if one's nearby) may be an option. If not, you'll want to power it from the main AC distribution panel using marine-grade, multistranded, three-conductor AC wiring. Pick an unused circuit breaker of the amperage called for by the charger manufacturer (typically 15 to 20 amps) and connect as per the instructions.

Practice safe wiring by making sure all AC power sources (including inverters and generators) are off and disconnected before starting any work! When all the connections have been made (and with the AC power off), make the final charger connections to the battery and verify the installation is complete. Once that's done, all that's left is to energize the AC circuit, power up the charger, and bask in the glow of success!

Testing the charger

Testing your onboard battery charger is a straightforward process. Here's a step-by-step guide to help you determine if your charger is functioning correctly:

Step 1: Disconnect the Positive Lead

First, disconnect the positive lead from both batteries. This will ensure that you can safely work on the battery and charger connections without any risk of a short circuit.

Step 2: Check the Water Level

Check the water level in each battery and add distilled water if necessary. Maintaining the correct water level is crucial for the proper functioning of your batteries.

Step 3: Measure Initial Battery Voltage

Using a voltmeter, measure the voltage of each battery and note the readings. This initial voltage measurement will serve as a baseline for comparison after you connect the charger.

Step 4: Connect the Charger Leads

Connect the charger leads directly to the battery, ensuring a secure and proper connection. A loose connection can affect the charging process and provide inaccurate results.

Step 5: Power Up the Charger

Turn on the battery charger and let it run for a few minutes. This will allow the charger to start its charging cycle and begin supplying power to the batteries.

Step 6: Measure Battery Voltage Again

After a few minutes, measure the voltage of each battery once more. If the charger is working correctly, you should see an increase in the voltage readings compared to the initial measurements in Step 3.

Step 7: Repeat for the Other Battery

If you have a dual battery system, repeat the entire process for the other battery. This will ensure that both batteries are being charged effectively by the charger.

Step 8: Perform an Open Circuit Voltage Check (Optional)

You can also perform an open circuit voltage check on each output of the charger. However, without a load (the battery) connected, the readings may be inconclusive. This step is optional but can provide additional information.

Step 9: Interpret the Results

If there is no change in voltage readings after connecting the charger, it is an indication that the charger is not functioning properly. In this case, you may need to replace the charger or consult a professional for further diagnostics.

Additionally, it is important to note that the voltage readings you obtain will depend on the type of battery you have. A fully charged healthy marine battery should register between 12.6 to 12.7 volts. However, some AGM batteries can have readings up to 12.8 volts. It is crucial to refer to the specifications of your specific battery type when interpreting the voltage measurements.

Frequently asked questions