Nickel cadmium or VRLA for signalling, which and why?

NiCd tolerates a wider temperature range, deep discharge and long neglect better, which is why it persists in legacy signalling installations. Sealed gel VRLA is lower cost, needs no watering, is easier to handle and dispose of, and is explicitly permitted. The pragmatic position most Australian RIMs have reached is that sealed long-life cells should be used wherever possible, which is ARTC’s own wording, with NiCd retained where a specific installation or approval requires it. The deciding factors on a new installation are usually location-case temperature and the maintenance regime, not chemistry preference.