Lithium Ion Batteries on Small Craft

    In 2025, the first edition of ISO 23625 Small Craft: Lithium Ion Batteries was published. This standard does not set any detailed requirements for the storage and ventilation of lithium ion batteries. Instead, it requires only that:

    “In case of a failure mode that results in a cell venting, the battery installation shall allow for cell venting such that the safety of persons onboard is not endangered.”

    and

    “The safety philosophy for the energy storage space (ESS) shall be documented.”

    The standard does not prescribe, for example, if batteries may be installed in the accommodation or if they must be fixed in a metal box, vented to the exterior. These details are left to a documented safety philosophy, which we may call a risk assessment.

    HPiVS is currently co-authoring ICOMIA’s Guide on Risk Assessments for the small craft industry. This will be released in 2nd quarter of 2026. Until then, please approach HPiVS to discuss methods of risk assessment. There are many!

    This page points out HPiVS’ minimum expectations and provides information for others to use in an informed risk assessment.

    Cell Quality

    Some say “modern, good quality cells are safe”. But how does one recognise good or bad quality cells within a battery when it is on a shelf in the shop? ISO 23625 provides the answer. Cells shall conform to:

    • IEC 62619 Safety requirements for secondary lithium cells and batteries, for use in industrial applications, and
    • IEC 62620 Secondary cells and batteries containing alkaline or other non-acid electrolytes

    HPiVS will not certify boats with lithium ion batteries whose documentation fails to confirm conformity with these standards.

    Ventilation

    One feature that is clear is that ventilation shall be provided in some form. This is clear because ISO 23625 says we must keep people safe should a cell vent. But should the batteries be provided with dedicated/independent ventilation to the exterior or is it enough to vent into a vented space? 

    The current edition of the standard does not demand that batteries have their own independent vent lines to the exterior unless the battery manufacturer or the risk assessment require it.

    Cell Technology

    Again, some say that “LFP batteries are safe and it is only other technologies we need to worry about.”

    If it was that simple, ISO 23625 would distinguish between different cell technologies. It does not, but a risk a assessment can.

    Accident statistics from a number of industries bear testimony that some battery technologies are less likely to vent than others. For some technologies, it is certain that runaway follows venting, whereas others may vent a cell without concern of runaway.

    Note that the requirement to keep people safe refers to “a cell” – a single cell – venting, not an entire battery in runaway.

    So, if a risk assessment shows that for a specific battery and installation, the calculated risk of runaway is tolerable, then the boat manufacturer needs only to be concerned with venting of a single cell.  See ‘ventilation’ alongside.

    Battery manufacturer installation specifications shall be met

    The standard demands that the batteries shall be fitted according to the manufacturer’s instructions. These might cover the following:

    • Location (e.g. not in a habitable space)
    • Ventilation (e.g. direct to exterior)
    • Distance from other batteries of sources of heat and vibration
    • Temperature or cooling
    • Means of fixing in position

    There is not much consistency between manufacturers with regards to installation instructions. If is not clear, ask them.

    HPiVS will not certify boats with lithium ion batteries where the manufacturer cannot show they have followed the battery manufacturer’s installation requirements.

    Reference Points

    The following tables are offered merely as a reference point for risk assessments.

    Standards

    Standard
    Sector
    Requirement
    AS/NZS 3001.2:2022
    Caravans, motorhomes, campervans, camper trailers, and similar mobile units
    lithium batteries in living areas must be in a dedicated compartment vented to the exterior or in a compliant, sealed enclosure to manage potential fumes.
    UK MGN 550
    Craft being used commercially
    Batteries shall be located within either a steel plated battery box or room with A60 fire integrity, or equivalent.
    ISO 23625:2025
    Recreational craft with hull length < 24m.
    Installation must keep people safe when a single cell of a lithium battery is venting. Risk assessment required to consider all risks, including thermal runaway.
    ABYC E-13
    Boats up to 24m in length
    No specific requirements for installation other than away from sources of heat, physical damage and as per manufacturer’s instructions.

    Statistics for Risk Assessment