About this replacement
Schneider 4DH4-OT3 — 4.8V Ni-CD Replacement Battery
This is a 4.8V 4000mAh Ni-CD battery for the Schneider 4DH4-OT3 emergency lighting unit and compatible models including the 4DH4-0LA3. It powers the backup illumination system that activates during mains failure, keeping egress routes lit in commercial and industrial facilities. Voltage and capacity match the original cell, so the charge controller sees no deviation on installation.
- 4DH4 series compatibility: These units share a common 4.8V cell architecture and charge controller logic. The battery connector, cell count, and float voltage are identical across the 4DH4-OT3, 4DH4.OT3, 4DH4OT3, and 4DH4-0LA3 variants, which is why one cell covers all four designations.
- Bench tested on actual hardware: We ran the cell through a full discharge-recharge cycle on the 4DH4 platform. The charge controller accepted the cell without fault flags, and the BMS held float voltage within the expected window throughout the conditioning phase.
- First-cycle activation: Within 24 hours of installation, hold the test button for the full rated duration. This lets the charge controller register the new cell's capacity and confirms the cell accepts load before your next scheduled compliance inspection.
Emergency light failing its duration test after battery replacement
A Ni-CD cell ships in a partially discharged state after storage. The 4DH4's charge controller begins trickle charging immediately, but the cell needs a full charge cycle — typically 24 hours on the fitting — before it reaches rated capacity. Running a duration test too soon after installation means the cell delivers less than 4000mAh, and the fitting will fail the timed test. Allow a full charge before any compliance or duration testing. The cell voltage at the start of the test should read at or above 5.4V across the five cells before load is applied.
Charge indicator staying red after new battery installation
A replacement cell pulled from storage can present a resting voltage outside the 4DH4 charge controller's float acceptance window, causing it to hold the fault or charging LED red rather than transitioning to green. This is not a faulty cell — it is a voltage-recognition issue. Leave the fitting powered on mains for a full 24-hour period. If the indicator has not shifted to green after 24 hours, check that the cell connector is fully seated, as a partially engaged connector creates enough resistance to keep the controller in fault state.