Lithium-ion battery guidance

Lithium-ion batteries on board

Lithium-ion batteries are significantly lighter and smaller than a lead acid battery of the same kWh, and generally have a longer lifespan than lead acid batteries. Additionally, as more of the battery’s capacity can be used, the same capacity lithium-ion battery should provide more energy than a lead acid battery. However, care needs to be taken to ensure lithium-ion batteries are used safely to mitigate the associated risks. 

Always follow the battery manufacturer’s instructions and recommendations

The risks when charging lithium-ion batteries can be greater than when charging lead acid batteries.

Battery manufacturers will specify how to use their products safely. With so many different devices and systems on the market, it is important to read the manual and follow the manufacturer’s instructions and recommendations. 

Portable devices

Whether you are using and charging small portable everyday devices (e.g. toothbrushes, mobile phones, cordless power tools, etc.) or larger portable devices (e.g. electric outboard motors, battery-powered water toys, e-bikes or e-scooters), care needs to be taken if the device has lithium-ion batteries installed.

The Boat Safety Scheme (BSS) provides guidance for lithium-ion batteries which, although developed with inland waterways in mind, is equally valid in the maritime setting https://www.boatsafetyscheme.org/stay-safe-advice/lithium-ion-battery-safety/.

The BSS guidance highlights the importance of looking after the device and charging it safely making sure you:

• Use the charger provided by the manufacturer
• Remember, charging too many devices can overload the boat’s systems
• Don’t leave portable devices charging unattended (i.e. only charge them when you are on board)
• Disconnect devices once fully charged

It is recommended you include information about charging devices on board in your safety briefing, particularly if you have someone on board for the first time.

Lithium-ion battery fires

If you are charging lithium-ion batteries on board, it is essential to be aware of the fire risk. A working smoke alarm can provide valuable early warning of a problem.

Lithium-ion battery fires are difficult to extinguish – traditional fire extinguishers may not work. They can spread rapidly - it is essential to be aware of this and keep escape routes clear.

Retro-fitting lithium-ion batteries on board

The installation of lithium-ion batteries can be complex and even dangerous if not done correctly. 

Don’t mix batteries with different chemistries

Mixing batteries with different chemistries within one charging system can be problematic if they have different charging characteristics. To prevent imbalances in charging and discharging, which can lead to dangerous situations, don’t mix batteries with different chemistries.

Whether replacing a ‘house’ battery or a battery in a propulsion role, be wary of batteries which are advertised as ‘drop-in replacements’. Different batteries have different requirements for optimal charging (this is their voltage, charge algorithm or charge profile). For example, if a lithium-ion battery has a different charging profile to the lead acid battery it is replacing:

• the charging system may not activate the battery management system and there is a risk of overcharging
• the alternator may burn out if it cannot cope with the current the lithium-ion battery draws or the rapid close down when they are fully charged.

It is generally recognised that lithium iron phosphate (LiFePO₄ / LFP) batteries are more robust and less sensitive than other chemistries and as such are often seen as more suitable for installation on board boats.

Hazardous gases and fire risk

Lithium-ion batteries can experience thermal runaway unless very precisely controlled. Thermal runaway is when a battery or component experiences a self-sustaining uncontrollable increase in temperature, often leading to catastrophic failure which can result in gas venting, smoke, or fire. It is important to understand that, when compared with a lead acid battery, the gasses released by a lithium-ion battery are more hazardous, the fire risk is different, and battery charging must be more carefully managed.

When a boat is designed, anticipated risks should be minimised. A boat designed for lead acid batteries should have:

• ventilation to minimise the risks posed by the release of hydrogen during charging;
• the batteries housed in a box to minimise the risk the acid poses to the people on board; and
• often the batteries will have a cover to ensure the battery terminals cannot be accidentally short-circuited.

The risks with lithium chemistry batteries are different. If a boat has not been designed for lithium-ion batteries and lithium-ion batteries are retrofitted these new risks must be identified and minimised:

• Lithium-ion batteries are sensitive to voltage changes so they have battery management systems to protect them, which may come with redundancies. This means if a lithium-ion battery fails it may give off highly toxic gasses. Appropriate ventilation for this scenario is essential. To achieve this, ventilation pathways may need rerouting.
• The fire risks are of a different nature, so existing firefighting solutions become redundant and must be replaced with solutions suitable for lithium-ion batteries.

Why DIY propulsion installations are not recommended

When installing lithium-ion batteries, being familiar with a 12 or 24 volt boat system isn’t sufficient. You need a more in-depth understanding of the technology to install lithium-ion batteries than for lead acid batteries.

Different lithium chemistry batteries have different requirements and risks which must be understood when installing them.

The risks associated with lithium-ion batteries can be minimised in a boat setting if the batteries are installed professionally with an appropriate battery management system. Your insurer may require lithium-ion batteries to be professionally installed.

Many manufacturers require installation through one of their registered installers for warranty purposes, particularly for electric propulsion systems.

It is really important to recognise if your knowledge isn’t sufficient and seek help from a professional.

Don’t forget:

• Make sure installed batteries are properly secured in their installed position.
• If a battery becomes damaged, take it off the boat at the earliest opportunity if it is safe to do so. Make sure you dispose of it correctly. It may need to go to a specialist recycling centre for safe disposal. If you can’t take the battery off the boat safely yourself, leave the boat and seek help from a professional.
• Changing the installed batteries in your boat can result in your boat needing to be recertified under the Recreational Craft Regulations. RYA Members can access our RCR guidance at https://www.rya.org.uk/members-legal-advice/buying-owning/boat-ownership/recreational-craft-regulations-directive-rcrrcd/.
• Tell your insurer about changes you make to your boat and follow any requirements. If you don’t you may find that your insurance is invalid.
• If you are the owner or managing agent of a coded vessel, consult your Certifying Authority prior to making any changes and follow any requirements. If you don’t you may find your code certificate is invalid.