Testing Boat Batteries: Are They Still Good?

Testing a boat battery is crucial to ensure a boat's safety and functionality. While it's easy to tell if a battery is completely dead, detecting an underperforming one is more challenging. Here are some methods to test if a boat battery is good:

- Using a Multimeter or Voltmeter: A multimeter or voltmeter can be used to test the voltage of a marine battery. A healthy battery should register between 12.6 to 12.8 volts when fully charged and not in use.

- Hydrometer: This method requires fully charging the battery and then not using it for a specified time, which can be inconvenient. The hydrometer is then inserted into each cell to take a reading.

- Solar Battery Tester: This tester can be used with 12-volt conventional lead-acid batteries and provides quick and accurate results.

- Open-Circuit Voltage Test: This test determines if your boat has a good power source by measuring the battery's state of charge using a multimeter.

- Voltage-Drop Test: This test checks for voltage loss in the circuit over time, which can be caused by faulty connections or corroded terminals.

- Continuity Test: This test determines if there is a break in the circuit, which could be due to a blown fuse or corrosion, by measuring the electrical flow in the system.

Using a hydrometer

Firstly, it is important to wear protective gear, such as gloves, safety goggles, a rubber apron, and closed-toe shoes. This is because the electrolyte in the battery contains sulfuric acid, which is highly corrosive and can cause injury or ruin clothing.

Next, move the boat to a well-ventilated area, turn it off, and remove the covers on the battery to access the electrolyte solution. It is important to remove all the covers at once, as drops of sulfuric acid might spring up from the battery.

Then, carefully insert the hydrometer into the cell and press on the bulb to draw the electrolyte into the device. The hydrometer should be filled to the maximum level. This step may need to be repeated several times to allow the thermometer in the hydrometer to adjust to the electrolyte temperature.

Once the hydrometer is filled, hold it vertically at eye level and note the reading where the electrolyte meets the scale on the float. This number represents the specific gravity of the electrolyte in the battery.

To interpret the results, note that a higher specific gravity indicates a higher charge state. A fully charged battery should have a specific gravity between 1.265 and 1.299. However, it is important to correct the reading for temperature, as the electrolyte solution expands when warm and contracts when cold, affecting the density and specific gravity. For example, for every 10-degree Fahrenheit difference from 80 degrees Fahrenheit (or 6-degree Celsius difference from 27 degrees Celsius), add or subtract 0.004 from the reading.

Finally, test each cell and note the readings, ensuring they are corrected to the standard temperature. A variation of fifty points between any two cell readings indicates a problem with the lower reading cell.

It is important to note that a hydrometer test requires the batteries to be fully charged and then not used for a specified amount of time, which can be inconvenient if the batteries are located in an inaccessible place. Additionally, the battery must go through at least one charge and discharge cycle after being watered to allow the water to adequately mix with the electrolyte.

Taking it to a battery shop for a load test

If you don't want to test your boat battery yourself, you can always take it to a battery shop for a load test. This is a tried and tested method, but it can be a bit of a hassle to remove the battery and take it to the shop.

Firstly, you'll need to locate the battery. On many boats, the battery is in the engine bay, but some manufacturers may have located it elsewhere. Check your owner's manual if you're unsure. Once you've found the battery, you may need to remove any plastic casing or covers. Be very careful not to touch both battery terminals with anything metal, as this will cause a short circuit.

Next, you'll need to disconnect the battery and take it to the shop. The staff there will be able to perform a load test to check its condition. They may use a hydrometer to test the battery, which requires the battery to be fully charged and then not used for a specified amount of time before testing. This can be inconvenient if your battery is located in an inaccessible place.

Another option is to use a solar battery tester, which is a much easier method that doesn't require you to disconnect the battery or let it sit unused for a long time. This type of tester can be used with 12-volt conventional lead-acid (wet cell) batteries, AGMs, spiral-wound AGMs, and gel cells. However, it's important to note that this tester can only be used with batteries that have a cold cranking amp (CCA) spec, which is usually printed on the battery or can be found in the manufacturer's information.

By taking your battery to a shop for a load test, you can get an accurate assessment of its condition and ensure that it's in good working order before your next boating trip.

Using a Solar Battery Tester

A solar battery tester is a huge step forward in keeping tabs on your boat's batteries. It can be used with 12-volt conventional lead-acid (wet cell) batteries, AGMs, spiral-wound AGMs, and gel cells.

To use a solar battery tester, you need to disconnect the batteries from one another and from any charging sources such as solar or wind. If the engine and/or generator aren't running, there is no need to disconnect, and any batteries that can be isolated by a switch don't have to be disconnected—only those that are connected within a single bank.

The next step is to connect the clamps on the tester to the positive and negative terminals on the battery. The tester will turn on using the battery's power. You then set the type of battery and input the cold cranking amp (CCA) specification, which can be found printed on the battery or on the manufacturer's website.

The tester will then run a quick test and tell you how many CCAs the battery currently has. If that number is less than half of the original number, it will indicate that the battery is bad.

The Solar BA5 Electronic Battery Tester is a good option for testing 12-volt batteries and typically costs between $50 and $60 online.

Checking the voltage with a voltmeter or multi-meter

Using a voltmeter or multi-meter is a good way to check the health of your boat battery. This test will determine if your boat has a good power source and tell you the battery's state of charge.

First, ensure your battery has been sitting for at least an hour before testing. This means it should not be on charge, or be charged through a boat or watercraft's split charging system. Ideally, leave your boat overnight, turning all systems off, and test the battery the next morning.

Next, locate the battery. It may be in the engine bay, or the manufacturer may have located it elsewhere. Check the owner's manual if you're unsure. The battery may be encased in a plastic box, shroud, or cover, which you will need to remove. Be careful not to touch both terminals with anything metal, as this will cause a short circuit.

Now, set your voltmeter or multi-meter to measure DC voltage. This is indicated with a dashed line and a solid line above a letter V. Set the dial to 20 to accurately measure between 0-20 volts.

Take the red probe and place it on the positive terminal of the battery, usually marked in red with a + symbol. Take the black probe and place it on the negative terminal, usually marked in black with a – symbol.

A fully charged, healthy marine battery should read between 12.6 to 12.8 volts. If your battery is fully charged but reads below 12.4 volts, it is considered flat and will need replacing. If your battery is reading below 12 volts, it is classed as discharged, and you will need to act fast to avoid deep discharge and sulphation.

If your boat is modern, it may experience 'parasitic loss', where your boat's electrical system continues to pull energy from the battery even when everything is turned off. If your boat is used infrequently or for short journeys, this can affect your battery's performance and service life. To check for this, fully charge your battery and then test it after letting it rest overnight.

Finally, you can also test your alternator with a multi-meter. With the engine running, place the probes of the multi-meter on the battery terminals. A healthy charging system should give a reading of between 13.6 volts and 14.4 volts at idle tick-over. If the reading is below 13.6 volts, your charging system isn't supplying enough power. If it's above 14.4 volts, it is over-charging and effectively cooking the battery, which will boil away the electrolyte. In either case, you will need to consult a professional to remedy the issue.

Checking for visible damage

Inspecting the Battery:

• Start by locating the battery on your boat. It is usually found in the engine bay, but some manufacturers may place it elsewhere. If you're unsure, consult your boat's owner's manual for the exact location.
• Once you've found the battery, carefully examine its exterior for any signs of damage. Look for cracks, warping, or bulging on the battery surface. These abnormalities indicate internal issues and are clear signs that the battery needs to be replaced as soon as possible.
• Pay close attention to the battery terminals, which are prone to corrosion. Corrosion is the buildup of a substance, usually green or white, on the metal parts of the battery. It can impede the flow of electricity and accelerate the deterioration of the battery.
• If you notice corrosion, it's important to clean it promptly. Use a wire brush or a cloth with a mixture of water and baking soda to remove the corrosive buildup. Regular cleaning can help prevent sulfation, which occurs when lead sulfate crystals form on the battery plates, hindering its performance.
• Aside from corrosion, keep an eye out for any leaks or cracks around the battery terminals. These issues can lead to excessive fluid loss and impact the battery's overall health.

Interpreting the Findings:

• If you observe any visible damage, such as cracks, warping, or bulging, it's imperative to replace the battery immediately. These signs indicate internal problems that compromise the battery's integrity and reliability.
• Corrosion and leaks around the terminals also warrant immediate attention. While cleaning can mitigate the effects of corrosion, persistent or excessive corrosion may require battery replacement.
• Even if the battery appears physically intact, be mindful of other symptoms that may indicate a failing battery. These include slow engine turnover, faulty electronics, and inconsistent voltage readings.
• Remember that a healthy marine battery should register between 12.6 to 12.8 volts when fully charged and not in use. Readings below 12.4 volts indicate a battery that is not holding a charge effectively, and replacement should be considered.
• Additionally, consider the age of your battery. Marine batteries typically last around three to five years. If your battery is within this age range or exhibiting signs of aging, it may be wise to proactively replace it to prevent unexpected failures.

Frequently asked questions