About this replacement
Fujitsu LIFEBOOK U7311 — 14.4V Li-Polymer Replacement Battery (CP784743-03)
This is a 14.4V, 4150mAh (59.76Wh) lithium-polymer replacement battery for the Fujitsu LIFEBOOK U7311 and LifeBook U7310 notebooks. It cross-references OEM part numbers CP784743-03, FMVNBP251, FPB0351S, and FPCBP577. The cell matches the original voltage rail and connector pin-out required by the U7311 mainboard.
- U7311 and U7310 compatibility: Both models share the same battery bay dimensions, 14.4V power rail, and BMS handshake protocol — which is why a single cell covers both. The connector layout and EEPROM communication lines are identical across this generation of LIFEBOOK ultrabooks.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on a U7311 unit. The BMS accepted the new cell without fault codes, and the charge controller stepped through CC/CV phases cleanly with no thermal interrupts.
- Post-install recalibration for the U7311: After fitting, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets 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
The U7311 BIOS reads health data from the battery's EEPROM, which stores cycle count and state-of-health figures written by the original cell. When a new cell arrives, its EEPROM values don't match the BIOS's learned reference — so the system flags poor health even though the cell is fresh. This isn't a fault with the replacement; it's a calibration mismatch. Run one full discharge-to-hibernate then a complete uninterrupted charge to 100%, and the BIOS will rewrite its reference data against the new cell's actual capacity.
Laptop shuts down at 20–30% charge shown on screen
This happens when the fuel gauge IC is still calibrated to the old, degraded cell. It expects voltage to drop slowly at lower charge levels, but a new cell has a steeper voltage cliff under full CPU and display load — so the BMS cuts power before the displayed percentage reaches zero. The fix is a full calibration cycle: discharge the laptop under normal use until it hibernates on its own, then charge to 100% without interruption. After two to three of these cycles, the fuel gauge IC recalibrates to the new cell's discharge curve and the shutdowns stop. Confirm calibration is complete when the resting voltage at 100% reads 16.8V at the battery terminals.