About this replacement
Fujitsu LifeBook U937/U938/U939 — 14.4V Li-Polymer Replacement Battery (CP730401-01)
This is a 14.4V, 3450mAh (49.68Wh) Li-Polymer battery for the Fujitsu LifeBook U937, U938, and U939 ultrabook series. It replaces OEM part numbers CP730401-01, CP737634-01, FPB0340S, and FPCBP536. Fit is confirmed against the slim 6.90mm profile and connector pinout common to this U-series chassis.
- U937/U938/U939 platform compatibility: These three models share the same battery bay dimensions, connector layout, and BMS handshake protocol. Fujitsu used the same cell pack across the U-series refresh cycles, which is why multiple OEM part numbers cross-reference to a single physical unit.
- Bench tested on actual hardware: We ran this cell on a LifeBook U938 chassis and monitored BMS communication through the full charge cycle. The protection circuit responded correctly to charge termination at 16.8V and tripped as expected at the low-voltage cutoff under sustained CPU and display load.
- Post-install calibration on LifeBook U-series: After fitting this battery, run the unit down to hibernate cutoff — do not force a shutdown — 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 poor battery health immediately after fitting a new cell
The LifeBook U-series BIOS reads EEPROM data written by the original cell during its operational life. When a new cell goes in, that stored cycle count and capacity history no longer matches the fresh chemistry, so the BIOS flags the battery as degraded. This is a data mismatch, not a fault with the replacement. Run a full discharge-to-hibernate followed by a complete uninterrupted charge to 100%. After two to three full cycles, the fuel gauge IC recalibrates against the new cell and the health warning clears.
Laptop shuts down at 20–30% charge shown on the battery meter
This happens when the cell voltage drops sharply under combined CPU and display load before the OS fuel gauge has caught up. The BMS trips at its low-voltage floor — typically around 12.0V under load — while the software still shows 20–30% remaining. The gauge is reading a resting voltage curve that no longer matches actual load behaviour on a new cell. Run three full discharge and recharge cycles to let the fuel gauge IC map the new cell's actual voltage-to-capacity curve and the early shutdowns will stop.