ISO small craft standards for lithium-ion battery installations

Why is there an ISO standard for small crafts? A pleasure craft build in the EU must comply to the Recreational Craft Directive (RCD) 2013/53/EU. This directive mandates CE marking for recreational craft between 2.5 and 24 metres placed on the EU market. The Small Craft ISO standards can be used to comply with this directive.

This note addresses the scope and applicability of each standard, the technical requirements relevant to lithium battery systems, the positioning of MG Energy Systems products within this regulatory framework, and practical compliance considerations.

The three principal ISO standards addressed are:

All three standards are developed by ISO Technical Committee TC 188 (Small craft).

2. Standard descriptions

2.1 ISO 23625:2025 — Small craft — Lithium-ion batteries

The ISO 23625:2025 specifies requirements and recommendations for the selection and installation of lithium-ion batteries on boats, as well as requirements for safety information provided by the battery manufacturer. It applies to lithium-ion batteries and battery systems with a capacity greater than 500 Wh used on small craft for providing power to general electrical loads and/or electric propulsion systems.

There are some key areas covered by the standard. One of the major points is that it references to meet the requirements of IEC 62619 (safety) and IEC 62620 (perfomance) standards. These are widely used by other regulations such as ES-Trin and Lloyds battery type approval as a basic requirement. Although the tests and requirements are extensive.

Other key coverage areas are:

• Battery system design requirements – Mainly on a system level
• Battery Management System (BMS) functional requirements
• Thermal runaway mitigation
• Ventilation requirements for battery compartments
• Installation requirements (mounting, compartment design, access)

2.2 ISO 13297:2020 — Small craft — Electrical systems

The ISO 13297:2020 specifies requirements for the design, construction, and installation of DC and AC electrical systems on small craft. It covers:

• Extra-low-voltage direct current (DC) electrical systems operating at nominal potentials of 50 V DC or less
• Single-phase alternating current (AC) systems operating at nominal voltages not exceeding AC 250 V

Exclusions: ISO 13297 explicitly does not cover:

• Electrical propulsion systems (covered by ISO 16315)
• Three-phase AC installations (covered by IEC 60092-507)

2.3 ISO 16315:2026 — Small craft — Electric propulsion system

The ISO 16315:2026 addresses the design and installation of AC and DC electrical systems used for electrical propulsion and/or electrical hybrid propulsion (systems combining a rechargeable battery with a fuelled power source) on small craft. It applies to:

• Direct current systems less than 1,500 V DC
• Single-phase alternating current up to AC 1,000 V
• Three-phase alternating current up to AC 1,000 V
• Vessels up to 24 m hull length (per ISO 8666)

Relationship to ISO 23625: For electric propulsion vessels with lithium-ion batteries, both ISO 16315 and ISO 23625 apply concurrently. ISO 23625 governs the battery system requirements; ISO 16315 governs the propulsion system integration. Where ISO 16315 does not specify a requirement, ISO 13297 applies as the baseline for general electrical installation.

3. Applicability

3.1 Vessel scope

All three standards apply to small craft as defined by ISO/TC 188: vessels with a hull length up to 24 meters. This covers the majority of recreational craft (sailing yachts, motor yachts, catamarans, RIBs) and many commercial small craft.

Vessels exceeding 24 meters fall under classification society rules (DNV, Lloyd’s Register, Bureau Veritas, etc.) and are outside the scope. MG offers a battery solutions that have a class society product type approval. This includes the MG Master HV and RS230.

3.2 When each standard applies

3.3 New build vs. retrofit

• New builds: Standards apply directly through the design and construction process.
• Retrofits: Replacing lead-acid batteries with lithium-ion systems on existing vessels is considered a technical modification with safety-relevant implications. This may trigger post-construction assessment requirements under the Recreational Craft Directive.

4. MG Energy Systems product positioning

At MG Energy Systems we offer a wide range of product categories relevant to ISO small craft standards compliance. Note that we focus on the compliance of the products while the shipyard has the responsibility to comply at a system and installation level. We can provide advice and recommendations on methods to manage the fire hazards associated with lithium-ion batteries, as required by ISO 23625. The exact project-specific requirements are the responsibility of the shipyard, and the appropriate measures are typically determined through a risk analysis and/or the safety philosophy for the energy storage space.

4.1 MG product features relevant to ISO 23625, ISO 13297 and ISO 16315

• IEC 62619 & IEC 62620 compliance (ISO 23625 §4.6): All MG batteries in scope (LFP 24V series, RS Series) are tested and certified to IEC 62619 (safety) and IEC 62620 (performance). These certifications directly satisfy the baseline requirements of ISO 23625 (§4.6).
• No cell-to-cell thermal runaway propagation: Validated through IEC 62619 testing. The LFP chemistry and cell spacing design prevent propagation between cells. This is compliant with the IEC 62619 requirements that is the basic certification for the ISO 23625.
• Safety-Lock feature: IEC 62619 mandates that a battery system cannot be placed into operation until its safety has been validated. The MG Master BMS implements this via the Safety-Lock mechanism, which is active on both Master LV and Master HV.
• Integrated BMS: The MG Master LV and MG Master HV fulfill the requirements to monitor and control all connected Lithium-Ion battery modules with implemented cut-off conditions (ISO 23625 §4.4 and §4.5).
• Integrated main safety contactor: The MG Master LV and MG Master HV have integrated main safety contactors to protect the connected lithium-ion batteries by disconnecting loads and chargers. This can be triggered in case one of the parameters such as cell voltage or temperature is beyond is safe operating limits (ISO 23625 §8.4 and §8.5).
• Integrated gas exhaust (LFP-IP series): The LFP-IP enclosure includes a built-in pressure relief and gas exhaust path. This feature supports the ISO 23625 §7.2 and §7.4, which addresses the requirements for extracting the gasses in a fault condition not to accumulate in a confined space and not endanger any persons on board.
• Overcurrent and short-circuit protection: Current monitoring combined with fuses and automatic contactor disconnection is integrated in the MG’s Master BMSs. This satisfies ISO 23625 (§6.8) requirements for overcurrent protection and fusing coordination without requiring external coordination design.
• Communication via NMEA 2000: SoC, SoH, voltage, current, and fault status are available over NMEA 2000, supporting the monitoring requirements referenced by ISO 23625.

4.2 Shipyard’s responsibility of integration

• Safety philosophy (ISO 23625 §7.2): The arrangement of the energy storage system space must ensure the safety of passengers, crew, and vessel. The boat builder is responsible for the safety philosophy document covering at least the following potential hazards: gas development hazard, fire hazard, necessary detection, monitoring and alarm systems including ventilation, explosion hazard, ventilation handling in case of off-gas release and/or fire and external hazards like fire and water ingress.
• Gas extraction to open air (ISO 23625 §7.2 and §7.4): Any gas released by the battery during fault conditions must be safely extracted to a location where it cannot accumulate and does not endanger persons on board.

4.3 Certification summary

The following table gives an overview of the certifications and the applicable MG products.

4.4 Compliance mapping

The table below maps MG Energy products to ISO standard requirements.

4.5 Frequently asked questions

Is it necessary to install the batteries in a sealed and ventilated enclosure?

Installing batteries in a sealed and ventilated enclosure can be used to mitigate the risks of gas development, fire, and explosion hazards. For big battery systems it is quite common to place the battery modules in a sealed and ventilated enclosure or a separate room.

• The battery modules are tested for cell-to-cell thermal runaway propagation, which reduces the risk of a cell failure escalating into a fire.
• A sealed enclosure will protect the battery from external fires — this is a risk to consider if the batteries are not placed in a separate room and other equipment is located in close proximity.
• Ventilation is not required for safety reasons during normal operation. The LFP cells used are of the sealed type, so no gases will develop or vent during charging.
• Ventilation can be useful to control the temperature of the battery space.
• Ventilation is necessary during an off-gassing event and/or fire.
• The gases produced during off-gassing and fire (thermal runaway) can be combustible and toxic, so extraction to a safe outdoor location is necessary.
• Note that ISO 23625 requires batteries and system components installed in locations not subject to flooding to be weatherproof (IP55 or higher).

Does the fire suppression system require immersing the batteries in water, or should a specific extinguishing system be used (e.g., gas injection)?

Immersing the batteries in water is the safest and most effective option to suppress a fire in the battery space, though it is also the most costly. Our preferred water-based extinguishing methods are:

• Immersion in water
• Water sprinkler systems
• Water mist systems

The choice of method depends on the safety philosophy and the specific installation. Immersion in water is highly effective for a battery fire, but if the fire originates externally, sprinkler or water mist systems may be more appropriate as they also address fires outside the battery space.

Gas injection systems can also be considered. Their effectiveness varies significantly depending on the battery space geometry, gas type, ventilation configuration, and other factors. The key principle for controlling lithium-ion fires is extracting heat from the modules, thereby containing the spread.

Does the system require an emergency shutdown device?

There is no strict requirement in ISO 23625:2025 for an emergency shutdown switch in the lithium-ion system.

However, some surveyors may refer to §4.1, which states that the system shall comply with the requirements of ISO 13297. ISO 13297 §9.1 includes a requirement for a main battery isolator switch, which is primarily applicable to lead-acid based systems. This requirement is sometimes incorrectly interpreted as mandating an emergency shutdown device for lithium-ion installations.

5. Conclusion

The ISO small craft standards — ISO 23625, ISO 13297, and ISO 16315 — establish a layered compliance framework for lithium-ion battery installations on vessels up to 24 meters. Each standard addresses a distinct scope, and in many installations more than one applies concurrently.

5.1 Shared responsibilities

Compliance is not the responsibility of a single party. It is shared between the battery manufacturer, the system integrator, and the boat builder:

• MG Energy Systems supplies battery modules and BMS products that are independently tested and certified to the underlying standards referenced by ISO 23625 (IEC 62619, IEC 62620, UN 38.3). Within their defined scope, MG products satisfy the product-level requirements of the standard.
• System integrators are responsible for correct wiring, fusing coordination, communication integration, and ensuring that the installation meets the applicable requirements of ISO 13297 and ISO 16315.
• Boat builders and shipyards carry the primary responsibility for system-level and installation-level compliance. This includes the design of the energy storage space, thermal runaway mitigation strategy, gas extraction routing, fire detection and suppression, and documentation of the overall safety philosophy.

5.2 The safety philosophy as a central deliverable

ISO 23625 requires the boat builder to produce a safety philosophy document covering the energy storage space. This document is the cornerstone of the installation’s compliance case — it defines how identified hazards (gas development, fire, explosion, water ingress) are managed through a combination of design, detection, ventilation, and suppression measures.

MG Energy Systems can support this process by providing product-level data, certified test results, and technical guidance on how MG systems behave under fault conditions. However, the safety philosophy is site- and vessel-specific. The choice of mitigations — enclosure type, ventilation design, suppression system — must reflect the actual installation and cannot be determined by the component manufacturer alone.

5.3 Summary

For installations within the scope of the RCD and the ISO small craft standards, a compliant outcome requires close collaboration between all parties from the earliest design stage. MG Energy Systems products are designed to support this process: certified at the component level, equipped with integrated safety functions, and documented to simplify the boat builder’s compliance case. The remaining responsibility — translating product compliance into a safe, compliant installation — rests with the integrator and shipyard.

6. Disclaimer

This engineering note is provided for informational purposes only and does not constitute legal, regulatory, or certification advice. While every effort has been made to ensure accuracy, the information herein is based on publicly available standard descriptions and MG Energy Systems product documentation as of February 2026.

7. References

7.1 Standards

• ISO 23625:2025 — Small craft — Lithium-ion batteries
• ISO 13297:2020 (Ed. 5, Amd 1:2022) — Small craft — Electrical systems — Alternating and direct current installations
• ISO 16315:2026 — Small craft — Electric propulsion system
• IEC 62619 — Secondary lithium cells and batteries for industrial applications — Safety requirements
• IEC 62620 — Secondary lithium cells and batteries for industrial applications — Performance requirements

7.2 Regulatory framework

• Directive 2013/53/EU of the European Parliament and of the Council (Recreational Craft Directive)
• Regulation (EU) 2023/1542 (EU Battery Regulation)
• ES-Trin (European Standard laying down Technical Requirements for Inland Navigation vessels)

7.3 MG Energy Systems resources

• Knowledge base
• Download center