About this replacement
Fujitsu Stylistic Q616 / Q665 / Q738 / Q739 — 11.1V Li-Polymer Replacement Battery (CP785375-XX)
This is an 11.1V, 3400mAh (37.74Wh) lithium-polymer battery for the Fujitsu Stylistic Q616, Q665, Q738, and Q739 2-in-1 detachable tablet-laptop hybrids. It replaces OEM part numbers CP785375-XX and FPCBP479. Use it to restore capacity when the original cell has degraded and the device no longer holds a charge through a normal workday.
- Q616 / Q665 / Q738 / Q739 compatibility: All four Stylistic models share the same 11.1V battery rail, connector pinout, and BMS handshake protocol — that is why one cell covers the entire lineup. The EEPROM on this replacement carries the correct charge parameters for Fujitsu's charge controller on each of these boards.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a Stylistic Q665 unit. The BMS accepted the cell without fault codes, charge termination triggered correctly at capacity, and the protection circuit responded to over-discharge cutoff within spec.
- Post-swap calibration on the Stylistic Q series: After installing this battery, run the device down to hibernate-cutoff under normal use load — tablet mode with wireless active works well — then charge uninterrupted to 100%. This gives the Fujitsu fuel gauge IC a full reference sweep and clears the inaccurate health warning that appears in the BIOS after every cell swap.
BIOS reporting poor battery health immediately after installing this cell
The Fujitsu Stylistic BIOS reads health data from EEPROM stored in the outgoing battery. When a new cell is installed, that EEPROM data does not yet match the new cell's actual state, so the BIOS flags health as poor or unknown. This is a data mismatch, not a fault with the replacement cell. Running one complete discharge-to-hibernate cycle followed by a full uninterrupted charge lets the fuel gauge IC write fresh reference data. After that cycle, the BIOS health indicator will reflect the actual state of the new cell.
Stylistic Q series shutting down at 20–30% charge shown on screen
This happens when a degraded cell can no longer sustain voltage under combined CPU and display load — the cell hits a voltage cliff before the fuel gauge reaches zero. The OS percentage shown is based on an old fuel gauge calibration, not the cell's real remaining capacity. Replacing the cell removes the voltage cliff, but the shutdown will continue until the fuel gauge IC is recalibrated against the new cell's actual capacity. Run one full discharge to hibernate-cutoff, then charge to 100% without interruption — after that cycle the gauge and the cutoff threshold will realign.