A backup battery on a signalling project is not accepted because a datasheet looks adequate; it is accepted because a documented chain of requirements, tests and safety arguments shows that the power supply will keep safety-related functions alive - or force a safe state - under every foreseen condition. This final paper maps the qualification campaign for a sealed nickel-metal hydride wayside battery. It starts from the railway safety framework - EN 50126 for RAMS, EN 50128 for software and EN 50129 for safety-related electronic signalling systems - and shows where the backup source appears in the hazard analysis, the safety requirements and the SIL allocation: the battery and charger are items whose failure can defeat a safety function, so their reliability, fault behaviour and autonomy are themselves safety requirements with traceable evidence. It then layers the environmental and electromagnetic qualification: EN 50121 for railway electromagnetic compatibility so the pack neither disrupts nor is disrupted by axle-counter detectors and balise up-links, the EN 60068 / EN 61373 family for temperature, humidity, vibration and shock, and ingress protection for an outdoor cabinet. The battery carries its own dossier - IEC 61951-2 performance for sealed NiMH cells, IEC 62133-2 safety for portable sealed secondary cells, the railway rolling-stock battery framework of IEC 62973 (whose Part 4 is dedicated to secondary sealed nickel-metal hydride and whose general Part 1 defines the common test approach), stationary battery installation safety where applicable, and UN 38.3 for transport. The paper explains how these documents are integrated into the signalling safety file, why lot traceability and construction control matter as much as the type tests, and how a supplier that delivers complete, consistent NiMH evidence removes a recurring bottleneck from signalling approval.
EN 50129 requires a safety case demonstrating that the electronic signalling system meets its safety integrity requirement under defined fault and environmental conditions. The backup supply is identified in the hazard analysis because mains loss is a foreseen external event and the response - continued safe operation for the autonomy window, or controlled transition to a safe state - is a safety function. The battery's capacity, ability to deliver peak current, behaviour at low voltage and end-of-life characteristics therefore appear as verifiable safety requirements, not merely commercial specifications.
RAMS work under EN 50126 supplies the reliability and availability targets, including the probability that the backup is actually available when the mains fails (a function of self-discharge, charger health and the verification regime). EN 50128 governs any supervision firmware. The practical output is a set of traceable requirements - autonomy at end of life and minimum temperature, maximum permitted voltage sag during events, alarms for battery failure, and periodic proof-testing - each linked to a test or analysis in the safety file.
Signalling cabinets are unusually EMC-sensitive: axle-counter wheel detectors and balise/LEU up-link cables carry weak signals that must be read correctly in the presence of train-borne interference and traction return currents. EN 50121 (the railway EMC series, with emission and immunity parts for both rolling stock and the fixed installation) sets the limits and tests, and the battery/charger must not introduce conducted ripple, switching noise or transients onto the signalling bus that could corrupt detection or telegrams.
The first animated figure layers the compliance stack. Qualification therefore tests the charger's conducted emissions and the complete power subsystem's immunity to surge, burst, electrostatic discharge and radiated fields, with the battery present as it is in service. A well-designed sealed NiMH pack, being a passive electrochemical reservoir with no switching electronics of its own, tends to simplify rather than aggravate EMC; the charger is the active element that carries the design effort.
Wayside equipment is qualified to the fixed-installation environment using the EN 60068 test methods - high and low temperature operation and storage, damp-heat cyclic and steady-state, and vibration and shock appropriate to trackside locations (EN 61373 is the rolling-stock vibration reference and informs trackside practice near the rail). The battery is tested at the extremes that matter most for autonomy: cold cranking of the load at the minimum cabinet temperature, and high-temperature float endurance that bounds calendar life.
Ingress protection and corrosion resistance keep moisture, dust and salt-laden air out of connections; thermal cycling tests look for contact drift and seal integrity. Crucially, the autonomy demonstration is repeated cold and on aged cells, because a room-temperature test on fresh batteries proves neither the derating nor the end-of-life guarantee that the safety case claims.
The cells and pack carry a layered dossier. IEC 61951-2 defines performance tests for portable sealed rechargeable nickel-metal hydride cells - capacity, charge retention, internal resistance and endurance - which characterise the building blocks. IEC 62133-2 provides safety requirements for sealed cells and batteries under expected use and foreseeable misuse. For the railway context, the IEC 62973 series addresses rolling-stock auxiliary batteries: Part 1 gives general requirements and test methods, Part 2 covers nickel-cadmium, and Part 4 is dedicated to secondary sealed nickel-metal hydride, giving designers and test houses a railway-recognised NiMH reference even though the immediate application is lineside rather than on-board.
Stationary battery installation safety (the EN/IEC 62485 family, successor to the EN 50272 series) is applied where the cabinet installation is treated as a stationary battery system, governing ventilation, protection against short circuit and mounting. UN 38.3 transport testing applies to shipment; sealed NiMH is non-lithium and is generally simpler to ship than lithium cells, a practical advantage when deploying spare packs to remote trackside sites.
The type-test programme demonstrates the claims end to end: a measured autonomy discharge using the real load profile (quiescent baseline plus the defined crossing or point events) at the minimum temperature and with cells conditioned to the end-of-life capacity floor; charge-retention testing to prove the pack is still ready after the maximum idle interval; periodic pulse/peak-current tests showing the bus stays above cut-out; and overcharge, external short, vibration, shock and thermal tests per the safety standards.
The second animated figure sequences this campaign. Endurance is demonstrated through the standard's cycle and float regimes rather than a single discharge, and lot consistency is established by sampling so that any replacement pack drawn from stores behaves like the qualified unit. The supervision and alarm logic is tested by simulated mains-loss and battery-fault scenarios, confirming that the signalling system reacts safely and that maintenance is summoned before autonomy can no longer be guaranteed.
Signalling approval lives or dies on traceability. The safety file records the exact cell type and manufacturer, the pack bill of materials and protection devices, the derating calculations and their assumptions, the environmental and EMC test reports, the battery performance/safety/transport certificates, and the rules for replacement - because substituting an unqualified cell changes autonomy and fault behaviour and can invalidate the case. Construction control (consistent welding, fusing, insulation and enclosure) keeps field units identical to the qualified type.
A battery supplier that understands this regime provides matched, construction-stable sealed NiMH cells with complete IEC 61951-2, IEC 62133-2 and UN 38.3 paperwork, supports the railway-specific IEC 62973-4 evidence, characterises low-temperature and pulse behaviour on request, and maintains lot traceability over the project's long life. That is the difference between a battery that merely fits the cabinet and one that survives the EN 50129 assessment and keeps controlled balises, axle counters and interlockings safe on the dark, cold night when the mains actually fails.
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.
