About this replacement
Fujitsu Lifebook U77 — 14.4V Li-Polymer Replacement Battery (FPCBP372)
This 14.4V, 3100mAh (44.64Wh) lithium-polymer cell replaces the OEM battery in the Fujitsu Lifebook U77 ultraportable notebook. It matches the original connector, dimensions, and BMS handshake the U77 motherboard expects. OEM part numbers FPCBP372 and FMVNBP220 both cross-reference this cell.
- Lifebook U77 fitment: The U77 uses a thin Li-Polymer pack in a flat sled form factor — 258.00 x 100.40 x 6.90mm. The BMS communicates with the BIOS over SMBus, so the connector pinout and EEPROM data structure must match exactly. This cell carries the correct SMBus-compatible firmware the U77 BIOS interrogates at boot.
- Bench tested on actual hardware: We cycled this cell through charge, idle, and load on U77-compatible hardware. The BMS reported state-of-charge correctly, charge termination triggered at the expected voltage, and no fault codes appeared during the SMBus handshake.
- First-cycle calibration on the U77: After fitting, run the laptop on battery until it hibernates at the low-voltage cutoff, then charge uninterrupted to 100% without interruption. This completes the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.
BIOS reporting battery health as poor after fitting a new cell in the U77
The U77 BIOS reads health data stored in the battery's EEPROM — not the actual cell chemistry. When a new cell arrives, that EEPROM data doesn't match the learned baseline the BIOS built against the old pack. The system flags it as degraded before any real wear has occurred. Running a full discharge-to-hibernate then a complete uninterrupted charge resets this baseline. After one or two full cycles the health indicator normalises.
Laptop shuts down at 20–30% charge shown on the U77 fuel gauge
This happens when the fuel gauge IC hasn't yet calibrated against the new cell's actual discharge curve. The IC maps voltage to percentage using data from the old cell — the voltage cliff comes earlier than the gauge expects, and the system cuts out. It is not a fault in the new cell. Run two to three full discharge and charge cycles without interruption, and the fuel gauge IC will recalibrate its voltage-to-capacity map. After calibration, shutdown should not occur above 5–8% reported charge.