About this replacement
RP-Technik 20109 LEX — 12V Ni-MH Replacement Battery (NH120)
This is a 12V, 700mAh Ni-MH replacement cell for the RP-Technik 20109 LEX emergency lighting unit. It slots into the fitting to restore backup illumination during mains failure or evacuation events. Sourced to match the original NH120 specification, including the NIMH1208P reference used in some service manuals.
- 20109 LEX compatibility: The 20109 LEX charge controller runs a float voltage tuned for Ni-MH chemistry at this cell count. Swapping to a different chemistry or voltage rating trips the charge fault circuit. This cell matches the voltage rail and BMS handshake the fitting expects.
- Bench tested on actual hardware: We ran the cell through a full charge cycle and a duration load test. The charge controller accepted the cell without fault, and the BMS held voltage under the rated emergency load without dropping into cutoff prematurely.
- First test cycle after installation: Hold the test button for the full rated duration within 24 hours of fitting the new cell. This allows the charge controller to register the new cell capacity and confirms the cell accepts load before your next scheduled compliance test.
Emergency light failing its duration test after battery replacement
A fresh Ni-MH cell from storage has not yet been conditioned to its rated capacity. The charge controller on the 20109 LEX begins float charging immediately on installation, but the cell needs one complete charge-discharge cycle to reach full capacity. Running the duration test before that cycle completes will produce a shorter-than-rated output and a fail result. Fit the battery, let it charge for at least 24 hours, then run the full test — the cell should hold voltage above 10.8V through the rated period.
Charge indicator staying red after new battery installation
The 20109 LEX charge controller checks cell voltage before switching from fault to charge mode. A cell that has sat in storage may present a resting voltage outside the controller's float acceptance window, keeping the indicator red. This is not a faulty cell — it means the controller has not yet begun bulk charging. Remove the battery, wait 60 seconds, refit it firmly, and confirm the connector is fully seated. The indicator should shift to amber or green within a few minutes as the controller detects a valid cell voltage.