About this replacement
Fujitsu Stylistic Q665 / Q738 / Q739 — 11.1V Li-Polymer Replacement Battery (CP690859)
This is an 11.1V, 3400mAh (37.74Wh) Li-Polymer replacement battery for the Fujitsu Stylistic Q665, Q738, Q739, and Q616 series detachable tablets. It replaces OEM part numbers CP690859, CP690859-01, CP700540-01, FPB0326S, FPB0349S, and FPCBP479. Install it when the original cell has degraded, lost significant capacity, or stopped holding charge altogether.
- Stylistic Q-series compatibility: The Q665, Q738, Q739, and Q616 all share the same 11.1V cell architecture, connector pinout, and BMS handshake protocol — that is why one part number covers all four platforms.
- Bench tested on actual hardware: We cycled this cell through charge, full discharge to hibernate cutoff, and a second full charge. The BMS reported correct voltage at each stage and did not trip the protection circuit under sustained load.
- First-cycle calibration on the Stylistic Q-series: After fitting this battery, 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 these tablets.
Why the Stylistic Q665 shuts down at 20–30% after a battery swap
The fuel gauge IC still holds voltage-curve data from the old, degraded cell. When the new cell reaches a voltage point that the old profile mapped to 20–30% remaining, the firmware calls a low-voltage shutdown — even though the new cell has capacity left. Running one full discharge-to-hibernate, then a full uninterrupted charge forces the gauge IC to relearn the new cell's actual voltage curve. After two to three cycles the shutoff point tracks correctly.
BIOS reporting battery health as poor immediately after installation
The Stylistic Q-series BIOS reads EEPROM data written by the original factory cell, including cycle count and rated Wh. A replacement cell presents different EEPROM values, which the BIOS flags as degraded or unknown health. This is not a fault with the new cell — it is a data mismatch. Run the battery learn cycle described above; on most Q-series units the health status updates to normal within one full charge cycle after calibration.