Batteries are part of the critical systems in any sportfishing boat. They help keep boats floating and contribute to the operation of the vessel. Modern marine lithium batteries are a significant disrupter to the traditional rechargeable lead-acid batteries that have been around since 1859.

Why Choose Marine Lithium Batteries for Sportfishing Boats?

When someone says lithium battery, it is good to understand that there are many types of lithium battery composition available in the marketplace, such as Lithium Iron Phosphate, Lithium Cobalt Oxide, Lithium Manganese Oxide, Lithium Nickel Manganese Cobalt Oxide, Lithium Nickel Cobalt Aluminum Oxide and Lithium Titanate.

The most popular consumer lithium battery today is the lithium cobalt oxide (LCO) battery. They are used in cell phones, laptops, tablets, digital cameras, and many other consumer-facing devices. Misconceptions about lithium marine batteries come from people’s experience with LCO batteries, which are a different chemistry than marine batteries. Additionally, confusion often exists with battery type description since the words “iron” and “ion” are accidentally misunderstood when talking about a type of lithium battery.

Key Benefits of Lithium Batteries in Marine Applications

When it comes to batteries designed for the marine environment, the Lithium Iron Phosphate battery, or lithium ferrophosphate (LFP or LiFePO₄) is currently the most popular type. For this article we are referring to LFP marine-style batteries that can often take the place of traditional batteries and are offered in a standard marine case, and not the lithium batteries used in consumer goods.

Comparing Lithium and Lead-Acid Batteries for Reliability

Traditional lead-acid batteries contain metallic lead, lead dioxide, lead sulfate and sulfuric acid. A more modern Absorbed Glass Mat (AGM) battery contains the same components, but with the liquid acid absorbed into fiberglass mats instead of sitting as a free-flowing liquid. The trending marine Lithium Iron Phosphate battery/LFP/LiFePO₄ contains phosphate as the cathode material and a graphitic carbon electrode as the anode enchased in a lithium-salt-electrolyte solution (or a solid composite electrolyte) within a sealed case. The popularized name LiFePO₄ is derived from the name of the elements that are contained with this battery type – Li = lithium, Fe=iron and PO₄= phosphate.

How Marine Lithium Batteries Enhance Boat Performance

Compared with traditional battery technology, lithium batteries charge faster, last longer, and have a higher power density for more battery life in a lighter package. Lithium batteries are here to stay. The automotive EV market has provided battery manufactures the volume and data to design new batteries to power electric cars worldwide. Mass produced EVs began in 2011 and by 2023 over 1 million EVs were sold in the USA, and 14 million worldwide. While the marine market is much smaller, we can also benefit from the lessons learned and the technology developed in the EV market for lithium batteries for our boats. The popular LFP composition used in marine batteries is also becoming popular in the EV market, contained in 30 percent of EVs in 2023, including Tesla and Ford, and expected to quickly increase.

The LFP battery is now the best fit for marine use in most all applications except high current draw, such as starting some engines. A high current draw will be recognized by the lithium battery built-in battery management system (BMS) and may prevent the battery from supplying engine cranking amperage. More on the BMS later in this article. Note: There are a few special lithium batteries designed to start an engine, but not all are designed for this application.

Battery Management Systems in Marine Lithium Batteries

One of the most beneficial aspects of a lithium battery is its function as a “deep-cycle battery,” where you can discharge up to 100 percent of their rated capacity every time with no ill effects for 3000 to 5000 cycles (specifications vary by brand). Once depleted, they can be recharged five times faster than a traditional battery. These features make them an excellent choice for trolling motors, bow thrusters, electric fishing reels, DC powered Seakeepers and other high critical electrical systems on a boat. While most sportfish boats have a generator that can recharge the house battery bank, building a lithium house bank can give you increased capacity with lower size and weight.

As a benefit of the decreased size and weight, battery manufacturers have become creative in offering unique solutions to boaters. For example, battery manufacturers can offer a 24- or 36-volt battery in one single standard marine case (in place of two or three traditional batteries in series), such as the Dakota Lithium 36-volt 60ah battery, prefect for trolling motors, in a standard marine Group 31 case, with a weight of 44 lbs.

Safety Considerations for Using Lithium Batteries on Boats

Currently, all LFP marine batteries contain a built-in BMS. It could be external, but that’s not common anymore. In summary, a BMS is a computerized system to actively monitor and protect the battery, which manages cell balancing, low-voltage cutoff, high-voltage cutoff, short-circuit protection and elevated temperature protection, both for safety and for increased performance and longer life. A few more acronyms help us describe the job of a BMS.  The State of Charge (SOC) and State of Energy (SOE) are two crucial battery states, which correspond to available capacity and are carefully monitored and managed by a BMS. Some BMS systems can communicate via Bluetooth to a smartphone app, through NMEA 2000 to a chartplotter, or to a dedicated display or battery mounted screen. This data is critical in learning and analyzing the successful operation of a lithium battery system.

Standards for Lithium Batteries on Boats

The American Yacht and Boat Council (ABYC) ratified their standard E-13 in 2022, covering the installation of lithium batteries on boats. E-13’s recommendations take effect for systems manufactured or installed after July 31, 2023. The standard’s scope applies to batteries of 600-watt hours or greater. For a 12-volt system, that means systems with a capacity of 50 amp-hours or more. In summary ABYC indicates:

• Follow the battery manufacturer’s installation and usage recommendations.

• Batteries or cells shall meet the testing requirements of various standards from IEC, SAE, and UL.

• All battery systems shall have a BMS to provide battery cutoff if hazardous conditions exist.

Other details are contained in E-13 that need to be followed to comply with the ABYC standards for lithium batteries.

Recharging Marine Lithium Batteries: Best Practices

One of the most talked about details of lithium batteries is safety and understandably, especially due to confusion regarding the variety of battery types. One of the biggest drawbacks I hear about lithium batteries is the potential fire hazard. The many variations of lithium batteries get grouped together when it comes to safety, though they have quite different chemical compositions and therefore different safety concerns. The LFP and similar phosphate-based batteries offer superior chemical ingredients, and the mechanical structure is resilient to the well-publicized overheating and thermal events. Thus, LFP batteries provide an increase in safety over other lithium-ion batteries and the safety characteristics make it the only logical choice on recreational boats. (Battery University)

Lithium batteries are sealed batteries to keep the battery components inside and keep water out in the event of a splash or spray, though they are not designed to be used while submerged. When it comes to battery safety, consumer goods with lithium batteries are more likely to be a problem onboard a boat than specialized marine batteries. Exposure to excessive amounts of or submersion in saltwater can begin corroding and subsequently short circuiting the consumer battery which can then interact with internal solvents (for solvent-based batteries) and could cause a fire. Popular consumer goods such as phones, computers, toys, tools, bicycles, scooters, hoverboard etc. often contain the LCO type of lithium battery.

Case Studies: Sportfishing Boats Using Marine Lithium Batteries

A captain recently told me he smelled something unusual upon entering his sportfish salon early one morning, and his nose guided him to the cabinet where a satellite communicator was being re-charged overnight. Finding the device smoking like chimney, he quickly grabbed the unit with towels and threw it overboard which extinguished the potential fire. Who knows what would have happened if he had arrived a few hours later.

Last summer, near Key West, Florida, Linda Vella lost her life to a fire on board a 70-foot Princess Yacht that burned at the Perry Marina overnight. “Investigators believe the e-bike and its battery fell into the water earlier in the day of the fire,” according to The Keys Citizen’s report. “After retrieval of the bike, it was parked on the dock, but the (lithium) battery was removed and placed on a wooden cabinet inside the vessel. The cabinet also contained USCG-required safety flares, which were ignited after the wooden cabinet caught on fire due to the battery.” We can learn from a tragic event like this.

Battery Fires

I overheard a guy bragging that he has a Class D fire extinguisher on his boat (Class D is for extinguishing metal fires) and that it was the correct extinguishing agent to use on any lithium battery fire. While it is good to be prepared with all types of fire extinguishers, not all lithium batteries require a Class D fire extinguisher. An ABC dry chemical fire extinguisher can be used on a lithium-ion battery. The National Fire Protection Association says, “Firefighters should use water to fight a lithium-ion battery fire. Water works fine as a fire extinguishing medium since the lithium inside of these batteries is a lithium salt electrolyte and not pure lithium metal. Confusion on this topic stems from the fact that pure lithium ,like what you see in the table of elements, is highly reactive with water, while lithium salts are non-reactive with water.”

When it comes to portable consumer type fire extinguishers, Seafire, the well-known marine fire protection company, offers a special LiCELL portable fire extinguisher that is designed to combat lithium battery fires. The LiCELL uses Aqueous Vermiculite Dispersion (AVD) as the fire extinguishing agent, a new technology to effectively combat lithium battery fires. The vermiculite particles within the deployed mist are deposited on the surface of the burning battery to create a film over the top of the fire. The film instantly dries and, because the high aspect ratio platelet particles overlap and bind together, a non-flammable oxygen barrier between the fuel and the atmosphere is produced. This process has a cooling effect on the fuel source and, as the water content in AVD evaporates, the vermiculite platelets begin to build up and the fire is brought under control. While learning about this product, I was told by Seafire that the LiCELL extinguisher needs to be sprayed directly on the battery itself and not the battery box as we typically use on a boat. This brings the question on how to mount or contain lithium LFP batteries, since if there is a fire, it may be impractical for someone to open a marine battery box before discharging the extinguisher.

Many consumer goods with lithium batteries can be a fire hazard, and it is good to be prepared to battle an onboard fire from these devices. We can learn from the research the Federal Aviation Administration has conducted regarding personal electronic device fires onboard passenger aircraft. In summary, they advocate the use of a battery fire containment device and now Underwriters Laboratory provides testing and certification of these products. Additionally, airlines are training their staff and equipping aircraft with personal protective devices for the crew, like face shields, fire resistant gloves and the fire containment bags to battle a fire. These firefighting products would also be a good fit onboard most any boat as another tool for the safety of passengers, crew, and vessel.

Start Your Engines!

Here comes that BMS system again. Many are designed to shut down a lithium battery to limit a high amp draw, such as over 100 amps constant, or few hundred amps briefly. Many outboard engines and large diesel engines require a much higher amperage while starting the engine. There are a few lithium batteries designed for this dual-purpose role, and often have supercapacitors built into the battery case that can supply a big burst of power independently of the lithium cells, proving the cranking amperage when needed and acting like a regular lithium battery the rest of the time. In 2022, Mercury Marine was the first major outboard engine manufacturer who issued an advisory bulletin permitting a specific type and brand of Lithium Iron Phosphate battery to start a variety of listed Mercury outboard engines.

Re-charging Lithium Batteries

Re-charging lithium batteries is different than convention lead-acid batteries. The major differences are that the charging voltage is slightly higher for LFP batteries than for lead-acid. For example, A 12v lithium LFP battery fully charged to 100 percent will hold voltage around 13.3-13.4v. A similar lead-acid battery will be lower, approximately12.6-12.7v when fully charged. An LFP charger is a voltage-limiting device that has similarities to the lead-acid system. The differences with Li-ion are a higher voltage per cell, tighter voltage tolerances and the absence of trickle or float charge at full charge. While lead-acid batteries and chargers offer some flexibility in terms of voltage cut-off, manufacturers of LFP cells are extremely strict on the correct setting because Li-ion cannot accept overcharge.

Additionally, the lithium battery BMS will internally disconnect the battery from the charging source if a problem occurs, to protect the battery. While this sounds like a great protection system, a marine alternator would be damaged when suddenly disconnected by a lithium BMS. Fortunately, many of the marine electrical equipment manufacturers now offer a wide variety of devices that ease the implementation of lithium batteries into a traditional electrical system. Two product types are readily available, the DC-DC charger and a dedicated AC-powered lithium battery charger.

The DC-DC charger is best for recharging lithium batteries in a mixed environment, such as charging a lithium house bank on an outboard powered boat that also has lead-acid batteries for engine starting. The AC-powered lithium charger can supply the correct voltage and amperage to recharge a stand-alone lithium battery bank. Mixing battery types within a battery bank or mixing types on a single charger will cause problems with the lithium batteries and is not recommended.

While it is not a primary concern for most sportfish boats, LFP batteries are difficult or impossible to charge in cold or freezing weather. Special systems are available to warm or pre-condition the battery in cold weather. Additionally, exceptionally hot weather can hamper proper operation of LFP batteries, though the batteries BMS system is able to monitor and disconnect the battery in an extreme temperature situation outside of the recommend range.

Lithium LFP batteries are overall a reliable source of power and are much safer than lithium batteries of just a few years ago. While lithium batteries are not often a drop-in replacement for all your boat battery systems, they can certainly be an advantage in systems such as trolling motors, bow thrusters, electric reels, Seakeepers, house bank and other non-engine systems.