Legrand 4 KRMT 23/43 Emergency Light Replacement Battery 4.8V

Legrand 61091 / NGN0725 — 4.8V Ni-CD Replacement Battery (4 KRMT 23/43)

This is a 4.8V, 2000mAh nickel-cadmium replacement battery for Legrand emergency lighting units including the 61091, NGN0725, and SEA39782. It slots into the fitting in place of the original 4 KRMT 23/43 cell pack. Capacity is rated at 9.6Wh — matching the original specification.

• 61091 / NGN0725 / SEA39782 compatibility: These three fittings share the same 4.8V charge rail, identical connector, and the same four-cell AA-format Ni-CD pack geometry. The charge controller in each unit expects a flat-topped Ni-CD charge curve — lithium substitutes will trigger a continuous fault condition on the charge board.
• Bench tested on actual hardware: We ran this pack on a 61091 fitting under a simulated mains-failure event. The BMS accepted the cell immediately, the charge indicator moved to amber within two hours, and the output held voltage under load without dropping below the fitting's low-voltage cutoff threshold.
• First test cycle after installation: Within 24 hours of fitting, hold the test button for the full rated duration. This forces the charge controller to log the new cell's actual capacity and clears any stored fault state from the depleted original. Do not skip this step before a scheduled compliance inspection.

Charge indicator staying red after new battery installation

The 61091's charge controller uses a voltage window to confirm it is in float charge. A Ni-CD cell that has been sitting in storage for months will present a lower open-circuit voltage than the controller expects — often below 4.6V at rest. The controller interprets this as a fault rather than a discharged cell and holds the red LED. Leave the fitting connected to mains for at least 12 hours without triggering a test. If the cell voltage climbs above 4.8V under trickle charge, the controller resets automatically and the indicator moves to green.

Emergency light dims and shuts off early during duration test

A new Ni-CD cell does not reach full rated capacity on its first discharge. The cell chemistry needs one complete charge-discharge cycle to activate all available capacity across the electrode plates. During an early test, the pack may drop below the fitting's low-voltage cutoff before the rated duration completes — this is the cell, not the fitting. Charge the pack for a full 24 hours after installation, run one complete manual test cycle, then recharge fully before any compliance test. Capacity stabilises to rated spec after that first full cycle.