Legrand 121420 Emergency Light Replacement Battery 3.6V 2000mAh

Legrand 121420 Series — 3.6V Ni-CD Replacement Battery (061032 / MGN9005)

This is a 3.6V 2000mAh nickel-cadmium cell for Legrand emergency lighting units including models 121420, 134896, 800980, and 800985. It slots into the fitting and connects to the onboard charge controller that maintains float charge between mains failures. Voltage and capacity match the original Legrand specification so the controller charges the cell without modification.

• 121420 and related fittings: These models share the same 3.6V single-cell NiCd architecture, connector type, and BMS float charge profile. A replacement cell on any of these fittings will register correctly with the charge controller without rewiring.
• Bench tested on actual hardware: We ran this cell through a full charge cycle and a load discharge under emergency lighting draw. The charge controller accepted the cell, completed the charge cycle, and the indicator shifted to green at the expected float voltage.
• First activation after installation: Hold the test button for the full rated test duration within 24 hours of fitting the new cell. This lets the charge controller register actual cell capacity and resets the compliance test baseline before the next scheduled check.

Emergency light failing its duration test after battery replacement

A freshly installed NiCd cell ships in a partially discharged state after months in storage. The charge controller begins trickle charging immediately, but full capacity is not available until the cell has completed at least one full charge and discharge cycle. Running a duration test too soon after installation will show a shorter illumination period than the cell is actually capable of. Allow 24 hours of mains-connected charging before conducting a formal duration test — the cell should reach its rated 3.6V float plateau by that point.

Charge indicator staying red after confirmed correct installation

Some Legrand fittings latch the fault state in firmware and do not automatically clear the red LED when a new cell is detected. This happens because the controller saw a low-voltage or open-circuit condition while the old cell was failing, and the fault flag persists until manually reset. On most fittings in this range, press and hold the test button for three seconds with mains power applied — this clears the latched fault and allows the controller to re-evaluate the cell voltage. If the LED returns to red after the reset, check cell voltage directly at the connector terminals; a healthy charged cell reads above 3.5V.