About this replacement
Fukuda FX-4100 / FCP-4101 Series — 9.6V Ni-MH Replacement Battery (8TH-2400)
This is a 9.6V, 3500mAh Ni-MH replacement battery for the Fukuda FX-4100 defibrillator line. It fits the FX-4100, FX-4211, FCP-4101, and FCP-4102 — all units that use the OEM part number 8TH-2400. Capacity matches the original at 33.6Wh.
- FX-4100 and FCP series compatibility: These models share the same 9.6V eight-cell Ni-MH architecture and a common BMS handshake protocol. The connector pinout and charge termination signal are identical across the range, so one cell pack covers all listed units without modification.
- Bench tested on actual hardware: We cycled this pack through full charge and discharge on a FX-4100 unit. The BMS accepted the cell chemistry, completed charge termination at the correct delta-V threshold, and passed the device self-test without triggering a fault code.
- Post-installation self-test protocol: After fitting this battery, allow the FX-4100 to complete its full power-on self-test without interruption. The device runs a BMS verification sequence at startup — cutting power mid-cycle writes a false battery fault to memory that persists until a clean reboot.
Self-test failure after battery swap on the FX-4100
The FX-4100's BMS stores chemistry calibration data from the previous pack. When a new cell is installed, the BMS has no learned capacity baseline to compare against, so it flags a self-test fault on the first boot. This is not a defective battery. Run one complete charge-discharge cycle and let the device finish its self-test undisturbed on the second boot — the BMS will write new calibration data and the fault clears. Do not place the unit in clinical service until that cycle is complete.
Low battery alarm triggers immediately after a confirmed full charge
The FX-4100 alarm threshold is calibrated to OEM cell internal resistance values. A new Ni-MH pack has higher internal resistance than a conditioned cell, which causes the device to read a lower effective voltage under load — even at full charge. The alarm clears after the first three to five full cycles as internal resistance drops to normal operating range. Confirm the pack reaches 10.8V off-load after a full charge before investigating further.