Fujikura FSM-50S Replacement Battery 13.2V 3500mAh Ni-MH

Fujikura FSM-50S / FSM-60S Series — 13.2V Ni-MH Replacement Battery (11HR-4/3FAU)

This is a 13.2V, 3500mAh Ni-MH replacement battery for the Fujikura FSM-50S, FSM-50R, FSM-60S, and FSM-60R fusion splicers. It replaces OEM part numbers including 11HR-4/3FAU, BTR-08, BTR-06L, and BTR-06S. The FSM-50S and FSM-60S are precision optical fiber fusion splicers used in telecommunications and fiber network installation.

• FSM-50 and FSM-60 platform compatibility: The FSM-50 and FSM-60 series share the same 13.2V battery bay, connector pinout, and BMS handshake protocol. One battery format covers both R and S variants across both model lines.
• Bench tested on actual hardware: We cycled this battery through charge and discharge on the FSM-60S bench unit. The BMS accepted the cell chemistry without fault codes, and the splicer completed its arc calibration sequence without interruption on the first cycle.
• Fusion splicer startup sequence: After installing a new battery, let the FSM-50S complete its full power-on self-test without pulling the battery or pressing any function keys. The splicer runs a BMS verification step at startup, and cutting power mid-sequence causes a latched battery fault that clears only on the next clean reboot.

Why the FSM-50S reports a battery fault after a fresh charge

The FSM-50S BMS uses a learned capacity threshold calibrated to the original OEM cell. A new replacement cell has not yet passed the BMS learn cycle, so the splicer may flag a battery warning even after a confirmed full charge. This is not a cell defect. Run one complete charge-discharge cycle — power the splicer on, let it operate until it prompts for charge, then charge fully — and the BMS resets its threshold to match the new cell. After that first cycle, the fault clears and does not return.

Charge indicator stuck below 100% on the first charge

On first charge, the FSM-50S charge IC applies a conservative current limit when it cannot confirm the cell's internal resistance profile. This causes the indicator to plateau at 90–95% and stall. Remove the battery, wait 60 seconds, reinsert it, and start a fresh charge cycle. The charge IC reinitialises its algorithm and typically reaches 100% within the second charge session. Target a resting voltage of 13.2V measured at the battery terminals before treating the first charge as complete.