Unitech 0253799 3.6V Emergency Light Replacement Battery

Unitech 0253799 — 3.6V Ni-CD Replacement Battery

This is a 3.6V, 800mAh Ni-CD cell built to replace part number 0253799 in Unitech emergency lighting units and exit signs. It restores the backup power function that keeps emergency lighting active during a mains failure. Dimensions are 52.10 x 27.00 x 26.60mm — confirm against your existing cell before ordering.

• Emergency lighting fit: Unitech emergency lighting units run a continuous trickle charge circuit that expects a Ni-CD cell at this voltage and capacity. Swapping chemistry or voltage breaks the charge controller's float window, causing persistent fault indicators or no-charge states.
• Bench tested on actual hardware: We ran this cell through a full charge cycle on the bench and confirmed the BMS accepted the cell voltage at float. The charge controller moved from charge mode to standby without triggering a fault output.
• Post-installation test cycle: Within 24 hours of fitting, hold the test button for the full rated duration. This confirms the new cell accepts load and lets the charge controller register cell capacity before your next scheduled compliance test. A new cell pulled from storage may not deliver full rated capacity on its very first activation.

Emergency light failing its duration test after battery replacement

A Ni-CD cell shipped from storage carries a partial charge, not a full one. The charge controller in Unitech emergency fittings applies a trickle rate that can take 24 hours or more to bring a new cell to full capacity. Running a duration test immediately after installation means the cell cannot sustain load for the full rated period, and the fitting fails. Allow at least 24 hours on mains power before conducting any compliance duration test on a newly installed cell.

Fault LED not clearing after confirmed good installation

Some Unitech emergency fittings latch the fault LED in hardware and do not clear it automatically once a new cell is detected. The charge controller needs to see the cell voltage rise above the float acceptance threshold before it resets the fault output. If the LED stays on after 24 hours of charging, locate the reset point on the fitting's control board — typically a small recessed button or a momentary short across two labelled pads. After a manual reset, the indicator should move to green once the cell voltage holds steady above 3.6V under float.