Lithium batteries on boats: What is important?

That was a close call! Literally at the last moment, the French professional sailor Fabrice Amedeo managed to escape from his burning Imoca racing yacht "Nexans, Art & Fenêtres" into the life raft during the "Route du Rhum" sailing regatta in November 2022. Previously, a ballast tank had broken during the storm. The water poured over the lithium-ion batteries and caused a short circuit. From Amedeo's report, it can be concluded that this was the cause of the fire that later broke out. After several hours in the life raft, Amedeo was rescued by the crew of a cargo ship.

However, it is not only on-board batteries, such as for the electric motor, that can cause the loss of a ship. In September 2018, the motor yacht "Kanga" burnt down near the Croatian coast. The crew noticed a fire in the dinghy garage, but could not extinguish it. They abandoned the vessel after the fire had spread to the entire yacht. The report from the Malta Marine Safety Investigation Unit later revealed that the fire had been caused by damaged lithium-ion batteries on foilboards. The crew actually had noticed the damage but had not removed the batteries from the boat.

In 2022 alone, several yachts have fallen victim to fires caused by defective batteries in surfboards or other water sports equipment. The fire hazard has to do with the characteristics of lithium-ion-batteries, which are the most common type of lithium batteries. Lithium-ion batteries are rechargeable and they are capable of storing large amounts of electrical energy in a very small unit. They are quickly charged, usually have a long service life and withstand many charging cycles. These qualities make lithium-ion batteries indispensable in many mobile devices and also boost their popularity on boats, used for example in electric outboard motors for dinghies.

Although we always casually and generally speak of the lithium battery, there actually is no such thing as "the one" lithium battery. Lithium batteries differ in terms of the electrode materials used - and not all of these materials are suitable to be used for lithium batteries on boats. The electrode materials are also important for the other qualities of the batteries. In principle, however, the types are similar.

A battery consists of several cells, depending on the power. Each lithium-ion cell contains a positive and a negative electrode, the anode and the cathode. Between them is an ion-conducting and usually liquid electrolyte. This guarantees the transport of the lithium ions between the electrodes during the charging or discharging process. Another important component is the separator. It prevents direct contact between the anode and cathode and thus protects against short circuits.

Modern lithium batteries that are used according to the manufacturer's instructions and that have been professionally installed are, of course, no ticking time bombs. This applies both to lithium batteries as on-board batteries and to mobile lithium batteries. However, in the event of a defect and especially if used or stored improperly, the rechargeable batteries can release their energy abruptly and uncontrolled and thus pose a significantly higher potential of danger than other types of batteries.

The uncontrolled release of stored energy is called thermal runaway. If this happens, the lithium-ion cells in the battery block heat up. One cell can reach several hundred degrees Celsius and thereby heat up other cells - a chain reaction occurs and the battery can explode!

However, this does not apply to lithium iron phosphate batteries. These react to short circuits in a similar way as conventional lead-acid batteries, which means that smouldering fires can certainly occur. The chain reaction of a thermal runaway, though, is ruled out due to lower combustion temperatures.

Burning Lithium-ion batteries are difficult to extinguish

Battery fires are difficult to control by conventional means. The reason is that if the chain reaction was triggered from the centre of a larger battery, it is almost impossible to reach the actual source of the fire with an extinguishing agent, e.g. water, to stop or contain the reaction. If one tries to cool such a module, the water only reaches the outer layers or the casing of the batteries. For smaller modules with fewer cells the situation is different. Here, external cooling usually has a direct effect on the reacting cells. In addition, toxic and flammable gases can be produced in the event of a battery fire, so that a deflagration can occur.

The risk of fire increases as soon as a lithium-ion battery is damaged. What is usually less relevant for on-board batteries can become a real problem with batteries of mobile devices, water toys or e-bikes: A mobile phone can fall on the floor quickly and an e-bike can tip over easily. Batteries that are bumped or damaged must always be replaced, especially if they are already defective. Deformed, outgassing or smoking lithium batteries pose an acute fire hazard.

Protect lithium-ion batteries from light, heat and water

Another cause of fire can be thermal stress, for example if the battery is stored or charged at temperatures that are too low or too high. Each type of battery tolerates a different temperature during storage. Crews can avoid fires on boats by not exposing lithium-ion batteries to extreme heat. Ideally, therefore, toys should not be stored for long periods in particularly hot environments and certainly not charged there - this also applies to direct sunlight.

According to the German Insurance Association, so-called deep discharge also frequently causes fires. Deep discharge is the complete discharge of the battery. Such a discharge can lead to cell damage and thus also to spontaneous combustion. A complete discharge of the battery can occur if you continue to use devices even though the battery is already at its minimum. In many modern devices, however, the electronics are programmed in such a way that a deep discharge is not possible. The battery can then no longer be used.

Lithium batteries should never be charged unattended for a longer period of time and should always be disconnected from the power source after the charging process. Only use original chargers from the manufacturer or chargers explicitly approved for use with the respective battery.

If lithium batteries are used as an on-board battery, for example for the boat engine, a permanent connection to shore power should be avoided in order to prolong the battery's life. A battery management system is also essential for safe operation. When charging batteries of e-bikes or water sports equipment on boats, it is essential to charge the equipment under supervision. In addition, the batteries should be checked for damage, deformation or leaks before each charging process.

Use smoke detectors and storage boxes

Real-life cases show that a battery fire releases electrolyte and solvent vapours before hot fire smoke is produced. These vapours are heavier than air and thus descend. Fire and smoke detectors should therefore be placed both on the floor and on the ceiling in places where larger lithium-ion batteries are installed or stored and charged.

To reduce the danger from defective batteries from drones, cameras or e-bikes, there are also special storage boxes that have long been used in industry. Some even have built-in charge management and extinguishing systems to detect and prevent battery fires. In any case, they ensure that a fire cannot immediately spread to the boat, leaving enough time to organise firefighting.

Lithium-ion battery fires are considered very difficult to extinguish. Attempts to fight these fires with a conventional ABC hand-held fire extinguisher are usually unsuccessful, as lithium-ion cells produce the oxygen needed by the fire themselves. In addition, the extinguishing agents used have too little cooling effect to interrupt the reaction that is taking place. Water has therefore become the extinguishing agent of choice, at least for the fire brigade. This is needed in large quantities.

But beware: Every battery fire has a high potential of danger. Only very small devices can be brought under control by oneself. A burning smartphone, for example, can be extinguished with plenty of water and then placed in a larger container filled with water to cool the battery and prevent re-ignition. Extreme caution must be exercised: the escaping gases are toxic and can be harmful to health if inhaled.

Battery fire? Leave the area

If a larger battery catches fire, it can fill rooms on the boat with smoke within a few seconds. Endangered persons should immediately seek safety and leave the affected area. There is a great danger of explosion when extinguishing with water. If possible, the local fire brigade should be alerted immediately.

If the smoke development allows it, throwing the battery overboard can deescalate the situation. This is illustrated by the case of a motor yacht insured with Pantaenius. In that case, the battery of an electric surfboard caught fire. Without suitable extinguishing agents, the crew's only option was to throw the already smoking battery into the water to avoid damage to the yacht. This, of course, would only be suitable where no neighbouring berth holders could be endangered and, in view of the possible environmental damage, it is the last possible option.

Alert firefighters

Not every fire of an electronic device is automatically a battery fire. However, it is not even obvious to professional fire fighters whether a lithium-ion battery poses an acute danger or not. If a battery is actually damaged and a fire breaks out, temperatures of more than 1,500 degrees sometimes occur. At such high temperatures, the extinguishing water is split into hydrogen and oxygen. This creates a highly explosive air mixture in a very short time, which can lead to a so-called oxyhydrogen explosion if it comes into contact with even the smallest source of ignition.

Devices that obviously have a larger lithium-ion battery should therefore always be handled with appropriate caution in case of fire. The distance when extinguishing must be as great as possible. If the fire brigade has been called to a fire, it is essential that the firefighters are informed about installed lithium batteries, e.g. as an on-board battery or in the drive of the tender.

If you are thinking about a lithium battery on your boat, you should consider only a modern lithium iron phosphate battery, where the danger of thermal runaway does not exist at all. But even then, before changing the battery in any way, check the wiring with the dealer or manufacturer whether the wiring, including the cable cross-sections, fuses and charging technology, are suitable for the new battery. If you are planning to change over, you should take advantage of the situation to thoroughly check your on-board electrics, because this is one of the most frequent causes of total loss due to fire.