Legrand 660971 Emergency Light Compatible Battery 4.8V 2000mAh

Legrand URA ONE 6 616 40 — 4.8V Ni-CD Replacement Battery (660971)

This is a 4.8V 2000mAh Ni-CD replacement battery for Legrand emergency lighting units, cross-referenced under part numbers 660971, 9342824, and HB00040TA. It fits the URA ONE 6 616 40, URA ONE 6 626 34/40, U21LED 6 616 10, and U21LED 6 626 07/10 series fittings. The battery provides backup power to maintain emergency exit illumination when mains supply fails.

• URA ONE and U21LED series compatibility: These fittings share the same 4.8V charge rail, physical cell pack dimensions (171 x 25 x 22.5mm), and connector pinout — which is why one battery covers both the URA ONE and U21LED ranges despite the different fascia designations.
• Bench tested on actual hardware: We ran this cell pack through charge and load cycles on a URA ONE fitting. The charge controller accepted the cell voltage without fault and the BMS handed off cleanly to the load circuit during simulated mains failure.
• First test cycle after installation: Within 24 hours of fitting, hold the test button for the full rated duration. Ni-CD cells from storage need one complete discharge-under-load cycle before the charge controller can accurately register capacity — skipping this step risks a false failure at your next compliance test.

Why the URA ONE fails its duration test even with a new battery fitted

Ni-CD cells ship in a partially discharged state after months in a warehouse. When the fitting first charges them, it reaches float voltage quickly — but that surface charge does not reflect true cell capacity. The charge controller on these fittings uses voltage thresholds, not cycle history, to assess readiness. A cell that looks charged at float can still collapse under the emergency lighting load within minutes during a duration test. One full manual test cycle resets this and lets the cell reach its rated 2000mAh working capacity.

Charge indicator staying red after a confirmed correct installation

Some URA ONE and U21LED fittings latch a fault condition in the charge controller firmware when the original battery voltage drops below approximately 3.6V before removal. Fitting a new cell does not automatically clear this flag. Disconnect mains power to the fitting for 30 seconds, then reconnect — this forces a charge controller reset and allows it to re-evaluate the new cell voltage. If the red LED persists after reset, measure the incoming mains supply at the terminal block and confirm it is within the 230V ±10% operating range the fitting requires to run the charge circuit.