Fukuda B11524 3.6V Replacement Battery FCP-4101 ECG

Fukuda Denshi FCP-4101 ECG Memory — 3.6V Li-SOCl2 Replacement Battery (B11524)

This is a 3.6V lithium-thionyl chloride cell rated at 1200mAh (4.32Wh), built to the B11524 specification. It fits the Fukuda Denshi FCP-4101 ECG Memory electrocardiograph, where it powers long-term memory retention of recorded cardiac data. Li-SOCl2 chemistry is specified here because of its very low self-discharge rate and stable voltage output over extended standby periods.

• FCP-4101 memory circuit compatibility: The FCP-4101 uses this cell specifically to sustain ECG data in non-volatile memory when the main power source is absent. The voltage rail sits at 3.6V nominal, and the BMS on this device expects the flat discharge curve characteristic of Li-SOCl2 — a lithium-ion cell at the same voltage would trigger premature low-battery flags due to the different discharge profile.
• Bench tested on actual hardware: We loaded the cell against a resistance profile matching the FCP-4101 memory circuit draw and confirmed the BMS accepted the cell without fault codes across the full startup sequence, including the power-on self-test.
• Post-installation self-test protocol: After fitting this cell, allow the FCP-4101 to complete its full power-on self-test cycle without interrupting power. The device runs a BMS verification pass at startup — cutting power mid-sequence forces a false battery fault flag that persists until the next clean reboot.

Why the FCP-4101 rejects a new Li-SOCl2 cell with a low-battery alarm

Li-SOCl2 cells form a thin lithium chloride passivation layer on the anode during storage. This layer temporarily raises internal impedance, causing the BMS to read a loaded voltage below its acceptance threshold on first installation. The FCP-4101 interprets this as a depleted cell and triggers the alarm immediately. The layer dissipates after a brief initial load — most devices clear the fault within one or two complete power cycles without any intervention.

FCP-4101 not powering on after the replacement cell sat in storage

Even at its low self-discharge rate, a Li-SOCl2 cell stored for an extended period can drop below the BMS recovery threshold the FCP-4101 uses to initiate startup. The device will not boot if the cell presents below approximately 3.0V under load, as the BMS blocks the startup sequence to protect the memory circuit. Connect the device to its external main power source first, let it stabilise for two to three minutes, then attempt to power on — this allows the main supply to bring the board up while the cell recovers. If the cell reads below 3.0V with a multimeter after removal, replace it rather than attempting recovery.