About this replacement
RP-Technik NIMH4805S.ST — 4.8V Ni-MH Replacement Battery (NH28S)
This is the NH28S 4.8V 600mAh Ni-MH replacement cell for RP-Technik emergency lighting units carrying the NIMH4805S.ST designation. It restores backup illumination function after the original cell has degraded or failed a duration test. Voltage, connector, and cell count match the original factory specification.
- NIMH4805S.ST fitting compatibility: The 4.8V rail maps to four series Ni-MH cells, matching the charge controller's float voltage window on this fitting. Swapping to a higher-capacity or different cell count will push the float charge outside the controller's acceptance range and trigger a permanent fault LED.
- Bench tested on actual hardware: We ran this cell through an initial charge cycle and a full load test on a NIMH4805S.ST fitting. The charge controller accepted the cell, transitioned from red to green within the expected window, and the BMS held voltage steady through a simulated mains-failure event.
- First test cycle after installation: Within 24 hours of fitting this battery, hold the test button for the full rated duration. This lets the charge controller register the new cell and confirms it can sustain load before your next scheduled compliance inspection.
Charge indicator staying red after fitting the new NH28S cell
The charge controller on RP-Technik fittings measures the incoming cell voltage before accepting it into float charge. A new Ni-MH cell shipped in a low-charge storage state will often sit below the controller's minimum acceptance threshold — typically around 4.2V for a 4.8V pack — and the indicator stays red. Leave the fitting connected to mains for 12–24 hours; the controller runs a conditioning current that brings the cell into acceptance range. If the LED has not moved to green after 24 hours, measure the cell voltage directly — a healthy cell should read at least 4.5V at rest by that point.
Emergency light passes installation but dims and cuts out mid-duration test
A new Ni-MH cell often needs one full charge-discharge cycle before it reaches its rated 600mAh capacity. On the first test activation the cell voltage sags under lamp load, the fitting's low-voltage cutoff trips, and the light extinguishes before the test duration completes. This is not a faulty cell — it is an unconditioned one. Allow a full 24-hour charge after installation, then run the duration test again. The cell should sustain the load through the complete test period on the second cycle.