About this replacement
Fujitsu Lifebook U904 Series — 14.4V Li-Polymer Replacement Battery (FPCBP412)
This 14.4V, 3050mAh (43.92Wh) Li-Polymer battery replaces the original FPCBP412 / FPB0305S cell in the Fujitsu Lifebook U904 ultrabook. It fits the U904, U9040M75A1DE, U9040MXPC1DE, U9040MXPA1DE, and related variants. The U904 is a thin-chassis business laptop, and the slim 6.80mm battery profile is specific to that enclosure — standard notebook cells will not seat correctly.
- U904 series fitment: All U904 variants listed share the same 14.4V power rail, the same connector pinout, and the same BMS handshake protocol. The FPCBP412 part number covers the full production run of this chassis, so one cell fits every model in the family.
- Bench tested on actual hardware: We ran this cell through charge, full-load discharge, and BMS cutoff on a U904 unit. The BMS handshake completed correctly, the charge controller accepted the cell without fault codes, and the cutoff voltage triggered cleanly at the expected threshold.
- Post-install calibration on the U904: After fitting, run one full discharge to hibernate-cutoff — let the laptop shut itself down — then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears on the first boot after every cell swap.
BIOS reporting poor battery health immediately after swap on the U904
The U904 BIOS reads health data stored in the battery's EEPROM, not live cell voltage. When a new cell is installed, the EEPROM data does not match the BIOS's accumulated charge history from the old battery, so the firmware flags it as degraded. This is a data mismatch, not a cell defect. Running one full discharge-to-hibernate followed by an uninterrupted full charge forces the BIOS to rewrite its learn-cycle data against the new cell. After one or two completed cycles, the health indicator returns to normal.
Laptop shutting down at 20–30% remaining after battery replacement
This happens because the fuel gauge IC is still calibrated to the old cell's discharge curve. The new Li-Polymer cell has a steeper voltage drop under combined CPU and display load than the worn cell it replaced, and the gauge misjudges where the actual cutoff sits. The laptop hits the real low-voltage threshold before the percentage readout catches up, triggering an abrupt shutdown. Run two full discharge-to-cutoff and uninterrupted full-charge cycles — after the second cycle, the fuel gauge IC recalibrates and the percentage readout aligns to the new cell's actual capacity.