About this replacement
Schneider VTD137 — 3.6V Ni-CD Replacement Battery (329030650)
This is a 3.6V 1500mAh Ni-CD replacement battery for the Schneider VTD137 emergency lighting unit. It fits the internal battery bay directly and connects to the charge controller using the original harness. Capacity matches the OEM specification at 5.4Wh.
- VTD137 fitting compatibility: The VTD137 charge controller floats the cell at a fixed trickle rate matched to Ni-CD chemistry. Swapping to a different chemistry breaks that charge curve and the fitting cannot compensate — this cell keeps the charge circuit operating as the fitting expects.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted charge from the first connection, voltage rose steadily through the Ni-CD plateau, and the cell delivered consistent output through a full rated discharge cycle.
- First-installation test cycle: Hold the test button for the full rated duration within 24 hours of fitting the new cell. This confirms the cell accepts load under real conditions and allows the charge controller to register the new capacity before your next scheduled compliance test.
Charge indicator staying red after new battery installation
A replacement Ni-CD cell shipped from storage typically arrives at a lower resting voltage than the float acceptance window the VTD137 charge controller expects. When the controller reads a voltage below its threshold, it holds the red fault indicator rather than switching to green. This is not a wiring fault or a dead cell. Leave the fitting connected to mains for 24 hours — once the cell charges above the acceptance threshold, the indicator will switch. If it does not switch after 24 hours, check cell voltage directly; a healthy charged Ni-CD should read at or above 3.6V.
Emergency light dims partway through a duration test
Ni-CD cells need at least one full charge-discharge cycle before reaching rated capacity — a cell installed and tested the same day will often fall short under load. The lamp dims because the cell voltage drops below the inverter's minimum operating threshold before the test duration is complete. Run a full 24-hour charge after installation, then repeat the duration test. A fully conditioned cell at 1500mAh should sustain lamp output through the complete test without voltage sag.