About this replacement
Thorn Voyager Star Cs 2 SBS — 2.4V Ni-MH Replacement Battery (59004661)
This is a 2.4V 2500mAh Ni-MH replacement battery for the Thorn Voyager Star Cs 2 SBS emergency lighting unit. It replaces OEM part 59004661 and fits directly into the fitting's battery bay. Capacity is rated at 6Wh — use the product data figure, not the original cell's label if it has faded.
- Star Cs 2 SBS fitting compatibility: The Star Cs 2 SBS uses a 2.4V two-cell Ni-MH pack with a specific physical footprint — 44.10 x 45.15 x 22.90mm. The charge controller in this fitting expects Ni-MH chemistry. Fitting a different chemistry will trigger a permanent fault LED because the charge profile will not match.
- Bench tested on actual hardware: We ran this cell through a full charge cycle and a timed load discharge. The BMS accepted charge within the expected float voltage window and held load without dropping below the cutoff threshold for the rated 6Wh capacity.
- First-cycle test requirement: Hold the test button for the full rated emergency duration within 24 hours of installation. This lets the charge controller register the new cell and ensures your next scheduled compliance test returns a valid pass — skipping this step is the single most common reason a freshly fitted battery fails its first duration test.
Charge indicator staying red after new battery installation
The Star Cs 2 SBS charge controller uses a float acceptance window to confirm the cell is taking charge correctly. A replacement cell that has been sitting in storage can present a resting voltage low enough that the controller flags it as a fault rather than beginning the charge cycle. This is not a defective cell — it is the controller rejecting a voltage it does not recognise. Leave the fitting on mains for 12 hours and check again; most cells recover to a voltage the controller accepts without any manual reset.
Emergency light dims and cuts out partway through a duration test
This happens when the new cell has not completed a full conditioning charge before the test is triggered. A partially charged Ni-MH cell at 2.4V will deliver rated output initially, then sag as stored charge depletes faster than expected. The fitting's undervoltage cutoff then trips the circuit before the rated duration is reached. Restore mains, allow a full 24-hour charge, then re-run the test — the cell should hold load for the complete rated period without dimming.