Brennstuhl AHL28 Emergency Light Replacement Battery 3.6V 2000mAh

Brennstuhl AHL28 — 3.6V Ni-MH Replacement Battery (90703101)

This 3.6V 2000mAh Ni-MH cell replaces the original battery in the Brennstuhl AHL28 emergency light. It fits directly to the AHL28's internal charge controller using the OEM part number 90703101. Capacity is rated at 7.2Wh — use the product data figure, not the original label if it has faded.

• AHL28 charge controller compatibility: The AHL28 uses a constant-trickle charge circuit sized for 3.6V Ni-MH chemistry. Swapping to a different voltage or chemistry trips the thermal cutoff on the controller board and the unit will not maintain standby charge.
• Bench tested on actual hardware: We cycled this cell through mains-on charge and simulated mains-fail discharge. The BMS accepted the cell without fault flagging, and the charge indicator moved from red to green within the expected window after a full conditioning charge.
• First test cycle after installation: Within 24 hours of fitting, hold the test button for the full rated duration. This lets the charge controller register the new cell's capacity baseline before any scheduled compliance test. Skip this and the controller may underestimate available charge.

Emergency light failing its duration test after battery replacement

A freshly installed Ni-MH cell ships partially discharged — typically 30–50% state of charge from storage. The AHL28's charge controller needs a full uninterrupted charge cycle, around 24 hours on mains, before the cell reaches rated capacity. If a duration test runs before that cycle completes, the light will cut out early and log a fail. Allow a full 24-hour charge, then run the test button hold from a cold start to confirm the cell delivers rated output.

Charge indicator staying red after new battery installation

The AHL28 charge controller checks incoming cell voltage at power-up. A cell that has sat in storage for months may read below the float acceptance window — typically under 3.0V open circuit — and the controller holds the fault state rather than entering normal charge. Leave the fitting on mains for two to four hours; the trickle stage will bring the cell voltage up into the acceptance band and the indicator should shift to green. If it stays red past four hours, measure cell voltage at the terminals — a reading below 2.8V after that period points to a cell that did not recover from deep discharge.