Lithium Fire Safety Boxes for Yachts: The Complete 2026 Guide to RACLAN Boxes, ZARGES Cases & MGN 681 Compliance

Between August 2021 and August 2022, 16 yachts were lost to fire. The MCA estimates that approximately half of the unexplained fires in that period are potentially attributable to lithium-ion battery failures (MGN 681, section 6). Lithium-ion fires are self-sufficient — they continue burning without additional oxygen — and produce off-gases including carbon monoxide, hydrogen, hydrogen fluoride, and hydrogen cyanide.

On 19 December 2025 the UK Maritime and Coastguard Agency published MGN 681 (M) Amendment 1, the first detailed guidance on storing and charging lithium-powered craft aboard yachts. This guide explains what MGN 681 requires, maps two verified product lines — RACLAN active safety boxes and ZARGES BatterySafe passive cases — to those requirements, and sets out the operational steps vessel operators need to take before the 1 January 2027 UK Type Approval deadline.

Mercer Yachting supplies lithium battery safety equipment for yachts from Malta, with delivery to any port worldwide. Request a quotation or read on for the full technical breakdown.

What MGN 681 (M) Amendment 1 Means for Your Vessel

MGN 681 (M) Amendment 1 is guidance published by the MCA that applies to yachts carrying small electrically powered craft — electric tenders, jet skis, e-foils, and personal watercraft — powered by lithium-ion batteries. It is based on the Red Ensign Group (REG) Yacht Code Part A, Chapter 14. The document establishes a clear precedence hierarchy: statutory requirements take priority over class rules, which in turn take priority over this guidance.

Key Thresholds

MGN 681 sets three battery capacity thresholds that determine what measures apply to your vessel:

• 100 Wh (section 4.2): Batteries exceeding this threshold trigger dedicated cabinet storage requirements. Spare batteries above 100 Wh must be stored in cabinets conforming to EN 14470, EN 16121, or EN 16122. Cabinets on open decks must be a minimum of 1.0 m from combustible materials, not placed on escape routes, and not adjacent to embarkation stations.
• 500 Wh aggregate: Crew awareness is required for smaller personal devices at this aggregate level.
• 10 kWh (section 4.23): This threshold triggers specific external storage and charging requirements for larger electrically powered craft.

For context, typical battery capacities in this sector are: e-foils 1–5 kWh, electric diver propulsion units 1–3 kWh, electric jet skis 20–50 kWh, and electric tenders 40–100 kWh. Most vessels carrying any of this equipment will exceed the 10 kWh threshold.

Temperature Limits

Ambient storage temperature must not exceed 45 °C (section 4.9). Thermal runaway initiation is estimated at 60–70 °C (section 6.3). The gap between maximum permitted storage temperature and thermal runaway onset is narrow — just 15–25 °C — which underscores why dedicated storage away from heat sources is essential.

Charging Space Restrictions

Charging spaces cannot be located (section 4.7):

• Forward of the collision bulkhead
• Inside Category A machinery spaces
• Adjacent to the main electrical power source

Batteries under charge must be a minimum of 1 m from these boundaries.

Structural Fire Protection

The required fire protection rating depends on vessel tonnage (section 4.11):

• A-60 for vessels of 500 GT and above
• A-30 for vessels below 500 GT
• B-15 for short-range vessels

Battery Conformity

Batteries above 100 Wh require a third-party conformity assessment — UKCA or equivalent — and must comply with IEC 62619 and/or IEC 62620 (section 4.4).

RACLAN Active Safety Boxes: How They Work

RACLAN produces active lithium fire safety boxes that combine containment with detection and suppression. Two models have verified specifications.

RACLAN Square

External dimensions	580 × 580 × 380 mm
Internal dimensions	540 × 540 × 235 mm
Battery capacity	Up to 3.5 kWh
Extinguishing agent tank	10 litres (TRIDENT®)
Certification	DMT TÜV Nord

RACLAN Box II

External dimensions	580 × 380 × 380 mm
Internal dimensions	540 × 340 × 200 mm
Battery capacity	Up to 1.754 kWh
Extinguishing agent tank	5.5 litres (TRIDENT®)
Certification	DMT TÜV Nord

Features Common to Both Models

Both the RACLAN Square and Box II share the following verified features:

• Fire-proof and explosion-proof high-tech composite material construction
• Acoustic alarm
• Optical function control
• Built-in emergency power supply
• Advanced exhaust system with toxin filter (hydrogen chloride filtration)
• Waterproof
• Stackable

How RACLAN Features Align with MGN 681 Charging Cabinet Requirements

MGN 681 sections 4.12–4.13 specify that charging cabinets must provide:

• Charging with cabinet closed — RACLAN boxes are designed for batteries to charge inside the sealed unit.
• Internal temperature rise detection — RACLAN’s optical function control and alarm system support this requirement.
• Extinguishing medium application without opening — The TRIDENT® agent deploys automatically within the sealed box (10 litres in the Square, 5.5 litres in Box II).
• Off-gas venting — The advanced exhaust system with toxin filter addresses this requirement, including hydrogen chloride filtration.
• Automatic charging stop on fault — Operators should verify this capability with the unit’s control system for their specific installation.
• Suitable insulation and explosion protection — The fire-proof and explosion-proof composite construction is aligned with these requirements.

RAMBSS: Modular System Now Available

The RAMBSS (Raclan Maritime Battery Safety System) is a modular, stackable system with interlinked modules, designed for larger vessels requiring multiple interconnected safety zones. Lloyd's Register Design Appraisal certified (DAD: TSO-24-013730-F01-DA), with WiFi monitoring and AMCS integration. Three module sizes available (up to 5.25 kWh). Request a quote or contact Mercer Yachting for specification.

ZARGES BatterySafe Cases: Storage and Transport

ZARGES BatterySafe cases provide passive containment for the storage and transport of lithium batteries. They are not active suppression systems; they contain thermal energy through material engineering rather than detecting and extinguishing fires.

Verified Specifications

Shell material	Aircraft-grade aluminium
Lining	Fixed intumescent Cirrux glass-fibre
UN certification	UN Packing Group 1 (highest level for hazardous materials)
Additional certifications	49 CFR, ATA 300 Category 1, IMDG
Testing	MIL-STD-810 tested; dust and water resistant
C-Series thermal containment	Tested up to 814 Wh
Weight (one model)	11.5 kg
Range	Multiple models/sizes: C-Series, F-Series, eFoil-specific

Important Limitation

ZARGES states that its BatterySafe cases are “not guaranteed to prevent thermal runaway from starting or spreading beyond the enclosure.” This is a critical distinction. ZARGES cases provide passive thermal containment for storage and transport, not active suppression. They are designed to buy time and limit damage, not to eliminate the event.

How ZARGES Cases Align with MGN 681 Storage Requirements

MGN 681 section 4.2 requires spare batteries above 100 Wh to be stored in dedicated cabinets conforming to EN 14470, EN 16121, or EN 16122. ZARGES BatterySafe cases — with their UN Packing Group 1 certification and MIL-STD-810 testing — support compliance with spare battery storage requirements within a vessel’s overall lithium battery safety arrangement. The operator should confirm with their surveyor that the specific ZARGES model selected satisfies the applicable EN standard for their vessel.

Choosing Between RACLAN and ZARGES

RACLAN and ZARGES serve different functions. Many vessels need both.

Criterion	RACLAN (Square / Box II)	ZARGES BatterySafe
Protection type	Active: detection, suppression (TRIDENT®), exhaust filtration	Passive: thermal containment via aluminium shell + Cirrux lining
Primary use	Charging and storage onboard	Storage and transport (on/off vessel)
Charging inside unit	Yes — designed for sealed charging	No — passive containment only
Maximum battery capacity	Up to 3.5 kWh (Square) / 1.754 kWh (Box II)	C-Series tested up to 814 Wh; multiple sizes available
Certification	DMT TÜV Nord	UN Packing Group 1, 49 CFR, ATA 300 Cat 1, IMDG
Thermal runaway guarantee	Active suppression; verify coverage with manufacturer	Explicitly not guaranteed to prevent thermal runaway spreading
MGN 681 alignment	Aligned with charging cabinet requirements (sections 4.12–4.13)	Supports spare battery storage requirements (section 4.2)
Construction	Fire-proof/explosion-proof composite; waterproof; stackable	Aircraft-grade aluminium; intumescent Cirrux lining; MIL-STD-810

When You Need Both

A vessel carrying an electric tender (40–100 kWh) and two e-foils (1–5 kWh each) will typically need:

• RACLAN boxes in the designated charging space for active protection during charging — the highest-risk phase of battery operation
• ZARGES cases for spare batteries not under charge, for damaged batteries awaiting offload, and for shore-side transport of batteries for service or disposal

Browse the full range of lithium fire safety equipment or request a quotation for your vessel.

The 1 January 2027 Certification Deadline

MGN 681 section 5 states that all battery storage and charging containers placed on board UK-registered vessels must be UK Type Approved by a UK Nominated Body from 1 January 2027.

What This Means in Practice

• Any container used for storing or charging lithium batteries onboard a UK-flagged vessel must hold UK Type Approval from 1 January 2027.
• Equipment purchased before that date should be verified with the manufacturer or supplier to confirm whether it will meet the forthcoming Type Approval requirement.
• Vessel operators should engage with their classification society and flag state administration now to understand what documentation will be required.

What Vessel Operators Should Do Now

1. Audit current equipment. Identify all lithium battery storage and charging containers currently onboard. Determine which hold third-party certification (DMT TÜV Nord, UN Packing Group 1, etc.) and which do not.
2. Confirm Type Approval pathway. Contact equipment manufacturers or your supplier to confirm whether specific models are on track for UK Type Approval.
3. Budget for replacement or upgrade. If existing equipment will not meet the 2027 requirement, plan procurement now to avoid supply bottlenecks as the deadline approaches.
4. Document everything. Maintain records of equipment certificates, purchase dates, and manufacturer correspondence. Surveyors will expect this documentation.

Crew Training and Operational Requirements

MGN 681 section 9 sets out crew training requirements. These are not optional guidance — they are part of the overall safety framework that surveyors will assess.

Required Training Areas

• Safe operation, storage, and charging of lithium batteries
• Identification of battery damage
• Disposal and quarantine procedures for damaged batteries
• Drills at agreed intervals

Named Responsible Person

MGN 681 recommends appointing a named responsible person for lithium battery safety onboard. This person should oversee compliance with storage and charging procedures, manage training records, and coordinate with the vessel’s safety management system.

Early Warning Signs of Thermal Runaway

All crew should be trained to recognise these indicators (from MGN 681):

• Sounds: Hissing, whistling, or popping from a battery or device
• Smell: A sweet chemical smell
• Visual — black “smoke”: Actually nanoparticles, not conventional smoke
• Visual — white vapour: Indicates off-gassing has begun

Off-Gas Hazards

During thermal runaway, lithium-ion batteries emit CO₂, CO, hydrogen, and volatile organic compounds. During an active fire, hydrogen chloride, hydrogen cyanide, and hydrogen fluoride may also be present. These gases are toxic and, in the case of hydrogen, flammable and potentially explosive.

Handling Damaged Batteries

MGN 681 is clear on damaged battery procedures:

• Store damaged batteries with extreme caution
• Unload at the first opportunity
• Never charge a damaged battery
• Be aware that damaged batteries may emit toxic and flammable gases even without visible signs of failure

Fire Detection and Suppression (Sections 7–8)

MGN 681 specifies the following detection and suppression infrastructure for battery storage and charging areas:

• Detection: Fixed smoke, heat, and gas detectors; CCTV at a continuously manned position; IR/thermal imaging is recommended
• Suppression: Automatic water-based system per SOLAS II-2; water-mist identified as most effective; minimum two portable extinguishers suitable for battery fires
• Ventilation: Mechanical ventilation extracting toxic and explosive gases, with capacity to remain below the lower explosion limit (section 4.16)

How to Specify Lithium Safety Equipment for Your Vessel

When preparing an RFQ for lithium battery safety equipment, provide the following information to ensure accurate specification and pricing.

RFQ Checklist

1. Device inventory with battery capacities. List every lithium-powered device onboard with its battery capacity in Wh or kWh. Include e-foils, electric tenders, jet skis, diver propulsion units, drones, e-bikes, and power tools. This determines which MGN 681 thresholds apply (100 Wh, 500 Wh aggregate, 10 kWh).
2. Vessel flag state and GT. This determines which structural fire protection rating applies (A-60, A-30, or B-15) and whether UK Type Approval will be required from 1 January 2027.
3. Proposed charging locations. Identify where batteries are currently charged and where dedicated charging spaces could be established. Remember: not forward of collision bulkhead, not inside Category A machinery spaces, not adjacent to main electrical power source (MGN 681 section 4.7).
4. Ambient temperature at storage locations. Storage must remain below 45 °C (section 4.9). Lazarettes and engine room-adjacent spaces in the Mediterranean summer regularly exceed this.
5. Number of spare batteries requiring storage. Any spare battery above 100 Wh needs dedicated cabinet storage per EN 14470, EN 16121, or EN 16122.
6. Transport requirements. If batteries need to be moved on or off the vessel (for service, disposal, or delivery), specify this — ZARGES cases with UN Packing Group 1 certification address this need.
7. Classification society and surveyor. Identify your class society so that equipment can be specified with the appropriate documentation for survey.
8. Existing fire detection and ventilation. MGN 681 sections 7–8 require specific detection (smoke, heat, gas, CCTV) and mechanical ventilation in battery areas. Note what is already installed.

Frequently Asked Questions