Saft 420735-00 Emergency Light Replacement Battery 3.6V 800mAh

Saft 420735-00 — 3.6V Ni-Cd Replacement Battery for Emergency Lighting

This is a 3.6V 800mAh Ni-Cd replacement cell for emergency lighting fittings that reference Saft part number 420735-00. It slots into exit signs and emergency fixtures that rely on a backup cell to illuminate evacuation routes during a mains failure. Voltage and capacity match the original specification exactly.

• Emergency lighting compatibility: Fittings using the 420735-00 share a charge controller calibrated for 3.6V Ni-Cd chemistry. Swapping to a different voltage or chemistry will push the charge voltage outside the controller's float window, causing either undercharge or overcharge over time.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on a Ni-Cd compatible analyser. The BMS accepted the cell without fault, charge current tapered correctly at top-of-charge, and the cell held load voltage above 3.3V through the discharge phase.
• First-installation test cycle: Hold the test button for the full rated duration within 24 hours of fitting this cell. A fresh cell from storage may not be at full charge. Running one complete test cycle lets the charge controller register the new cell capacity before the fitting logs it against a compliance record.

Emergency light failing its duration test after battery replacement

A new Ni-Cd cell ships partially discharged from storage. The fitting's charge controller starts a trickle charge on installation, but if a duration test runs within the first few hours, the cell hasn't reached full capacity yet. The light dims or cuts out before the rated duration ends — not a faulty cell, just an uncharged one. Allow the fitting to charge on mains for at least 24 hours, then repeat the duration test. The cell should hold load voltage above 3.3V for the full test period.

Charge indicator staying red after fitting a new cell

Some emergency fittings latch a fault condition in firmware when the old cell drops below the controller's acceptance threshold. Replacing the cell doesn't automatically clear the fault flag — the controller still sees the stored error. On most fittings, a 10-second press of the test button after a 24-hour charge cycle forces the controller to re-sample cell voltage and reset the indicator. If the fitting has a dedicated reset pin or reset sequence in its manual, use that instead. The charge LED should move to green once cell voltage reads above 3.5V at float.