Zumtobel 04879885 Emergency Light Replacement Battery 2.4V

Zumtobel 04879885 — 2.4V Ni-MH Replacement Battery (1538)

This is a 2.4V, 2000mAh Ni-MH cell that fits the Zumtobel emergency lighting fixture 04879885. It restores backup illumination capability when the original cell has degraded below the threshold needed to pass a full rated-duration test. Capacity is 4.8Wh as specified in the product data.

• 04879885 fitting compatibility: The 04879885 uses a 2.4V Ni-MH charge circuit with a fixed trickle float voltage. Substituting a cell outside that voltage window causes the charge controller to reject the cell or hold a fault state. This replacement matches the original cell's voltage, capacity, and physical format so the controller behaves as it did from factory.
• Bench tested on actual hardware: We ran this cell through a full charge cycle and a simulated mains-failure activation. The BMS accepted the cell without triggering a fault LED, and the load voltage held within acceptable range for the full test duration.
• First test cycle after installation: Hold the test button for the full rated duration within 24 hours of fitting the new cell. This lets the charge controller register actual cell capacity before the next scheduled compliance test — skipping this step means the controller may report a shorter usable duration than the cell can actually deliver.

Charge indicator staying red after new cell installation in the 04879885

The 04879885 charge controller checks cell voltage at startup before entering float charge. A cell that has sat in storage can drop below the controller's acceptance window — typically under 2.0V open-circuit for a 2.4V Ni-MH pack. When the controller sees that low voltage, it flags a fault rather than initiating a charge cycle. Connect the fitting to mains and allow 12–24 hours before drawing any conclusion about the red LED. If the LED stays red past 24 hours, measure cell voltage directly — it should be climbing toward 2.6–2.8V under trickle charge.

Emergency light dims partway through a duration test after fitting a new cell

A new Ni-MH cell straight from packaging has not yet reached its rated capacity — the first few charge-discharge cycles condition the cell and expand usable capacity toward the rated 2000mAh. If the light dims or cuts out before the rated test duration on the first test, the cell is not defective. Allow one full charge cycle of at least 24 hours on mains, then run the duration test again. On the second test the cell should sustain output voltage above the fitting's cutoff threshold for the full rated period.