Fujitsu U40-3S4400-G1L3 Replacement Battery 14.4V 2200mAh

Fujitsu LifeBook U40 — 14.4V Li-ion Replacement Battery (U40-3S4400-G1L3)

This is a 14.4V 2200mAh Li-ion battery pack for the Fujitsu LifeBook U40 ultraportable notebook. It replaces a degraded or failed original cell and restores full mobile use to the U40. Capacity is 31.68Wh, matching the original specification.

• U40 platform compatibility: All U40 variants share the same 14.4V three-cell series configuration and connector pinout. The BMS in each pack communicates over the same SMBus lines, so part numbers U40-3S4400-G1L3, U40-3S4400-C1M1, U40-3S4400-C1H1, U40-3S4000-G1B1, U40-3S4400-S1G1, U40-3S4000-S1S1, and U40-3S4000-S1L2 all reference the same physical and electrical form factor.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the U40 platform. The BMS communicated correctly over SMBus, charge termination triggered at the expected cutoff voltage, and the protection circuit responded normally to simulated over-discharge.
• Post-install calibration on the U40: After fitting this cell, run one full discharge to the hibernate cutoff point, then charge uninterrupted to 100% without interruption. This forces the BIOS battery learn cycle to reset against the new cell's actual capacity and clears the inaccurate health warning the U40 BIOS displays after every cell swap.

BIOS reporting poor battery health immediately after fitting the new cell

The U40 BIOS reads battery health from EEPROM data stored in the pack's fuel gauge IC. When a new cell goes in, that EEPROM contains manufacturer baseline data, not a learned profile for your specific system. The BIOS compares the reported data against its stored history and flags a mismatch as poor health. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% rewrites the learned data and clears the warning on the next boot.

U40 shutting down abruptly at 20–30% charge shown

This is a voltage-cliff failure, not a gauge error. Under combined CPU and display load, the cell voltage drops faster than the fuel gauge IC can track, and the pack hits the BMS low-voltage cutoff before the displayed percentage reaches zero. It happens most often in the first few cycles on a new cell before the fuel gauge IC has calibrated its discharge curve. Run two to three full discharge-and-charge cycles to let the IC build an accurate model of the cell's voltage-versus-capacity curve. If the shutdowns continue after three cycles, check that the BIOS is not applying a conservative cutoff at 11.1V rather than the standard 10.8V floor.