About this replacement
Fujitsu LifeBook B2620 — 10.8V Li-ion Replacement Battery (FMVNBP109)
This 10.8V, 4400mAh (47.52Wh) lithium-ion battery replaces the original cell in the Fujitsu LifeBook B2620 and closely related B-series notebooks. It also fits the LifeBook B2566, B2545, and B2175A, among others. OEM part numbers FMVNBP109, FMVNBP108, FPCBP36, and FPCBP37 all cross to this cell.
- B-series voltage rail compatibility: The LifeBook B2620 and its siblings in the B2000 and B2100 family share the same 10.8V three-cell architecture and identical connector pinout. The BMS handshake protocol is consistent across all listed models, so a single cell design covers the full compatibility range without any firmware or hardware variation.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on a LifeBook B-series unit and confirmed the BMS negotiated correctly with the system board. Charge termination fired at the expected cutoff voltage with no false trips or safety-flag errors reported in the system log.
- Post-install calibration for the B2620: After fitting this cell, run the laptop down to hibernate-level cutoff on battery alone — with the display at full brightness and a background task running — then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell and clears the inaccurate "poor health" warning that commonly appears after any cell swap on this platform.
Why the LifeBook B2620 shuts down at 20–30% after a battery swap
The B2620's BIOS tracks discharge curves from the previous cell and maps its shutdown threshold against that stored data. When a new cell is installed, the voltage-versus-capacity curve no longer matches what the firmware expects, so it triggers a low-battery shutdown while the cell still has usable charge. This is a calibration mismatch, not a cell fault. Running one full uninterrupted discharge-to-hibernate followed by a full charge corrects the curve mapping. After two or three cycles the gauge stabilises and premature shutdowns stop.
BIOS reports battery Wh as incorrect after fitting a replacement cell
The Wh figure shown in the BIOS or OS comes from EEPROM data embedded in the battery's BMS board, not from a live measurement. Some replacement cells carry EEPROM values that reflect the rated chemistry specification rather than the exact capacity of the installed cell, so the system may display a Wh figure that differs from the label. This is a data field discrepancy and does not affect actual charge delivery. To verify real capacity, run a full discharge cycle and compare the energy drawn against the nominal 47.52Wh figure — within 5% is normal for a new cell.