About this replacement
Fujikura FSM-12S / FSM-12R — 14.8V Li-ion Replacement Battery (BTR-10)
This 14.8V, 2000mAh Li-ion battery pack replaces the OEM BTR-10 and BTR-10-AC units in the Fujikura 12S series fusion splicer. It fits the FSM-12S, FSM-12R, and S015527 variants. Field technicians use the 12S to splice fiber optic cable away from AC power, so a functioning battery is non-negotiable on site.
- FSM-12S and FSM-12R compatibility: Both models share the same battery bay geometry, connector pinout, and BMS handshake protocol — the same pack serves either unit without modification.
- Bench tested on actual hardware: We cycled this pack through the 12S charge and discharge sequence, verified BMS communication across the data pins, and confirmed the splicer accepted the pack and displayed charge status correctly without error codes.
- First-use calibration on the FSM-12S: After installing the new pack, run a full splicing calibration cycle through the splicer's maintenance menu before heading to site. The 12S maps battery state during this process — skipping it causes premature low-battery warnings during your first arc discharge session in the field.
BMS cutoff during fiber alignment and arc discharge on the FSM-12S
The FSM-12S draws a sharp current spike the moment it fires the arc electrodes to fuse fiber. If the battery's BMS has a tight overcurrent threshold — common in aged or deeply discharged cells — it interprets that spike as a fault and cuts power mid-splice. The result is an aborted fusion and a splicer that appears to have shut down spontaneously. A replacement pack with a healthy BMS and full cell voltage handles that instantaneous load without tripping. Verify the pack reads at or above 14.4V before beginning a splicing session.
FSM-12S won't recognise a new pack after extended storage
If the splicer powers on but immediately displays a battery fault or fails to register the pack at all, the BMS has likely entered sleep mode after cell voltage dropped below its recovery threshold during storage. Connect the pack to the OEM charger and leave it for at least 30 minutes before attempting to power the splicer — most chargers will apply a low-current recovery charge below 12V. Once cell voltage climbs back above 12.8V, the BMS wakes, the handshake completes, and the splicer recognises the pack normally.