Philips Xenium S266 AB4000GWM Compatible Battery 3.85V

Philips Xenium S266 — 3.85V Li-Polymer Replacement Battery (AB4000GWM)

This is a 3.85V, 3850mAh lithium-polymer cell built to replace the AB4000GWM battery in the Philips Xenium S266 smartphone. It fits the Xenium S266 directly — same connector, same physical footprint at 88.60 × 60.40 × 4.06mm. Capacity figures come from the product data, not third-party estimates.

• Xenium S266 fitment: The S266 uses a specific low-profile pouch cell with a single-row connector tied to the phone's charge IC and fuel gauge. Swapping in a cell with mismatched impedance or connector pinout will prevent the BMS handshake from completing. This cell matches the original AB4000GWM connector layout and nominal voltage rail exactly.
• Bench tested on actual hardware: We cycled this cell through a full charge-discharge sequence on the S266 platform. The BMS accepted the charge handshake on the first cycle, and the fuel gauge IC registered a stable state-of-charge reading without requiring a manual reset.
• First-cycle fuel gauge recalibration: On first use after installation, disable fast charging for one complete discharge-charge cycle. The fuel gauge IC on the S266 is calibrated to the original cell's discharge curve. Running one slow cycle first lets the coulomb counter re-anchor to the new cell before fast charge pushes high current into an uncalibrated state.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff problem, not a capacity problem. Under modem load or screen-on draw, the new cell's voltage drops faster than the fuel gauge IC expects, crossing the cutoff threshold before the displayed percentage reaches zero. The phone shuts down to protect the cell even though the percentage still reads high. Run two full discharge cycles without fast charging — this lets the coulomb counter map the actual discharge curve of the new cell and push the apparent cutoff point back toward 0%.

Phone won't power on after the battery sat in storage

Lithium-polymer cells self-discharge in storage, and if the cell voltage drops below approximately 2.5V the BMS enters lockout mode to prevent cell damage. The phone will show nothing on screen — no charging indicator, no boot. Connect to a wall charger and leave it for 20–30 minutes without pressing the power button. Once the BMS sees voltage recover above its re-initialisation threshold, the charge indicator will appear and the phone will boot normally.