Saft 785509 2.4V Replacement Battery Ni-CD 1600mAh

Saft 785509 — 2.4V Ni-CD Replacement Battery

This is a 2.4V 1600mAh nickel-cadmium replacement cell for the Saft 785509 emergency lighting unit. It fits emergency exit signs and evacuation lighting fixtures that use the 785509 cell configuration. Voltage and capacity match the original specification: 2.4V, 1600mAh (3.84Wh).

• 785509 emergency lighting fit: The 785509 cell runs at 2.4V to match the charge controller's float voltage rail inside these fittings. Swapping to a cell at a different voltage or capacity causes the charge controller to misread state-of-charge and flag a fault. This cell keeps both parameters within the controller's acceptance window.
• Bench tested on actual hardware: We ran this cell through a full charge cycle and a simulated mains-failure discharge. The BMS accepted the cell without fault indication, held voltage under load, and returned to float charge cleanly after the discharge event.
• First-install test cycle: Within 24 hours of fitting, hold the test button for the full rated duration. This forces a complete discharge-charge cycle, allows the charge controller to register the new cell capacity, and confirms the cell accepts load before your next scheduled compliance inspection.

Emergency light failing its duration test after battery replacement

A freshly installed Ni-CD cell ships in a partial state of charge. The charge controller in most 785509 fittings does not run a conditioning cycle automatically — it simply maintains float once the cell voltage rises above the acceptance threshold. If a duration test is run before the cell has completed at least one full charge from a low state, available capacity will be lower than the rated 1600mAh and the light will cut out early. Allow a minimum 24-hour charge period after installation before running any compliance test. One manual test cycle after that charge period is enough to condition the cell and bring it to rated capacity.

Charge indicator staying red after confirmed good installation

Some 785509 fittings latch a fault LED in firmware when a low-voltage condition was previously detected — typically from the old depleted cell sitting in the fitting for an extended period. Fitting a new cell does not automatically clear the latch. The charge controller needs to see the cell voltage rise above approximately 2.3V–2.4V and hold there before it resets the fault flag. On most fittings, a brief power cycle — isolate mains supply for 30 seconds, then restore — clears the latched fault once the new cell is above that threshold.