Designing shipboard reserve power is governed by endurance that is written into international law and by an environment that punishes neglect. This paper develops sealed nickel-metal hydride reserve modules for the legitimate shipboard applications identified in the first paper - the GMDSS radio reserve under SOLAS Chapter IV/13, transitional sources and battery-backed emergency lighting and bridge/alarm loads - and works the sizing in the sequence a marine electrical engineer and classification surveyor expect. It begins with the load table and the regulated endurance: the radio reserve must simultaneously power the sea-area-defined VHF and MF/MF-HF/satellite fit for the required distress hour at the nominal 24 V, with transmit keying peaks superimposed on the watchkeeping baseline; emergency-lighting and transitional loads are summed over their own durations. It converts those energies to a delivered capacity after derating for the battery-room or fitting temperature, end-of-life fade and the voltage window of the radio or inverter, and it checks the transmit-peak current separately so keying cannot reset the radio. It then addresses installation: automatic connection on loss of supply, separation and protection so the reserve feeds only its intended loads, the charge regime that keeps sealed cells healthy through years of float in a rolling, vibrating, salt-laden hull, and the supervision and alarms that prove readiness. It compares sealed NiMH candidly with flooded lead-acid, valve-regulated lead-acid and nickel-cadmium under the IEC 60092 installation rules, IEC 60533 EMC and IEC 60945 equipment environment, showing where the sealed, maintenance-reduced, cadmium-free chemistry simplifies battery-room ventilation and upkeep, and where large traditional banks or the mandated primary batteries of survival craft remain the correct regulatory choice.
The radio-reserve calculation is load-based and simultaneous: list every radio the ship must operate for distress traffic by sea area (VHF always; MF for A2; MF/HF and/or Inmarsat/satellite for A3/A4), take the receive/watchkeeping current and the transmit current at the rated duty cycle, and sum them as they would actually be operated during the regulated endurance, which flag-state rules and IMO guidance express in hours (a one-hour minimum for the defined simultaneous fit is the familiar figure, with specific values set by the applicable regulation and whether an emergency source is fitted).
The first animated figure builds the radio energy budget. The battery must also supply any charging of the radio's internal batteries and the control/indicator load, and it must deliver the transmit peak - several times the receive current - without the 24 V rail sagging below the radio's cut-off. Capacity is then derated for temperature and end of life. The reserve is arranged to connect automatically, to be independent of the main and emergency sources, and to be protected against discharge by non-radio loads.
Emergency-lighting energy is the integral of the connected emergency fittings over the required duration - 18 hours cargo, 36 hours passenger for the emergency source, with the transitional battery covering the minutes before the emergency generator connects. The shift to LED fittings cuts the watt-per-lux dramatically, so distributed sealed NiMH packs in self-contained emergency fittings or local reserve boxes can now cover meaningful escape-route and embarkation-station lighting without a central flooded bank.
Transitional sources are power- rather than energy-dominated: they must instantly feed critical lighting and controls, and sometimes crank or support the emergency generator, for a few minutes after long idle. The sizing distinguishes this short high-readiness duty from the long flat lighting night and the radio hour, and applies the same cold/hot, end-of-life and voltage-window deratings with appropriate margins for survey.
The reserve connects to its load through a dedicated, protected distribution with automatic transfer on loss of the normal/emergery supply, clear isolation, and overcurrent and reverse-polarity protection; the GMDSS reserve is kept electrically independent as regulation requires. Charging is from a dedicated marine charger with current limiting, temperature compensation and a sealed-NiMH-appropriate float/top-up regime, because years of continuous charging at sea would otherwise overheat or dry sealed cells.
Low-self-discharge cells and a correctly managed charger keep the reserve genuinely full across long voyages and idle periods in port, while charge-current and failure alarms in the bridge or engine-control room satisfy the SOLAS readiness requirements. The 24 V nominal architecture aligns with marine radio and control practice, and fusing and cable sizing follow the IEC 60092 series installation rules.
Marine reserve modules must survive the IEC 60092/60945 environmental conditions: sustained vibration and shock, operation at defined angles of heel and trim, damp heat, dry heat and cold, and salt-mist corrosion. Construction uses restrained cells, anti-vibration mounting, welded or locked interconnections, corrosion-resistant hardware and conformal or sealed enclosures appropriate to the space, with terminals protected against spill and bridging.
Sealed NiMH's absence of free electrolyte removes the risk of acid spill under heavy roll and the need for electrolyte level inspection and topping-up in a moving vessel - a genuine maintenance and safety gain over flooded lead-acid and NiCd. Thermal placement still matters: reserve packs are sited away from direct engine heat and within the temperature range used for the capacity calculation, with the cold-start and hot-float extremes both verified.
Flooded lead-acid has long supplied large emergency and radio banks at low first cost, but requires a dedicated ventilated battery room or locker, electrolyte maintenance and spill containment, suffers in cold and from stratification/sulphation, and is heavy. VRLA reduces maintenance but remains cold-weak, can dry out under long float and heat, and still contains sulphuric acid. Flooded nickel-cadmium is the rugged premium choice - excellent extreme-temperature and abuse tolerance and long life - but needs watering, evolves gas, and carries cadmium under tightening environmental rules.
The second animated figure scores the chemistries on the axes that matter for distributed shipboard reserve: sealed/no-service, charge retention for instant readiness, cold delivery, ventilation burden and environmental compliance. Sealed NiMH matches much of NiCd's reserve-duty tolerance while being sealed and cadmium-free, and avoids lead-acid's maintenance and cold weaknesses - making it best suited to compact, distributed, maintenance-poor reserve modules rather than to replacing the very largest central banks.
A reserve battery is part of a regulated safety system, so the design dossier records the load calculation and endurance, the derating assumptions, the automatic-connection and charging arrangement, environmental construction and the cell standards, and it identifies the exact regulatory scope - distinguishing the ship-installed GMDSS reserve and emergency lighting (which the battery can serve subject to flag/class approval) from the survival-craft two-way VHF and EPIRB primaries (which it cannot).
The final paper maps the type-approval and survey campaign: SOLAS regulation and IMO performance standards, IEC 60945 for radio-adjacent equipment, IEC 60092 and IEC 60533 for installation and EMC, the MED wheel-mark where applicable, the IEC 61951-2 / IEC 62133-2 / UN 38.3 battery evidence, and the periodic inspections and drills that keep the reserve credible through the ship's life.
Weijiang Power designs and manufactures sealed nickel-metal hydride cells and matched industrial packs for remote, off-grid and safety-related equipment, and supports OEM partners with IEC 61951-2 performance files, IEC 62133-2 safety evidence, pulse-load characterisation, wide-temperature testing and charger/pack co-validation. Tell us your duty cycle, peak current, temperature envelope, autonomy target and the standards your product must meet, and our engineers will specify a cell-and-pack combination that protects runtime, reliability and service life. Review the range on the products page.
