MWG XDA IIS Replacement Battery 3.7V 4200mAh Li-ion

MWG XDA IIS — 3.7V Li-ion Replacement Battery (PH26B)

This 3.7V, 4200mAh Li-ion cell replaces the original battery in the MWG XDA IIS pocket PC phone. The XDA IIS is a Windows Mobile device from the mid-2000s, and original cells at this age have typically lost significant charge-holding capacity. This replacement restores full voltage delivery to the processor, radio module, and display.

• XDA IIS platform fit: The XDA IIS shares its battery bay dimensions and connector pinout with a narrow group of HTC-platform Windows Mobile devices from this era. Voltage regulation on the board runs directly off the cell — no intermediate buck stage — so correct cell voltage matters at load, not just at rest.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the XDA IIS platform and confirmed the BMS communicates correctly with the charge IC, holds cutoff at the expected low-voltage threshold, and does not trip under display and radio combined load.
• Fuel gauge recalibration on first use: On first use after installation, disable any fast-charge accessory and run one complete discharge-charge cycle at standard current. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before reporting percentages to the OS.

Sudden shutdown at 20–30% on the XDA IIS after a cell swap

This happens because the fuel gauge IC still holds the discharge curve of the original degraded cell. When the new cell hits a voltage point the old curve mapped to 20–30%, the IC signals a low-voltage shutdown even though real capacity remains. The fix is a single full discharge to auto-off followed by a full uninterrupted charge. After that cycle, the coulomb counter recalibrates and the reported percentage tracks the actual cell state correctly.

XDA IIS not powering on after extended storage

Lithium-ion cells left discharged in storage can drop below 2.5V per cell, which triggers BMS lockout — the protection circuit opens and blocks current flow to prevent damage. The device will show nothing on screen and will not respond to the power button. Connect to a wall charger rated at the correct output and leave it undisturbed for 20–30 minutes; the BMS recovery circuit needs a trickle current at or above 3.0V per cell to re-enable the main discharge path before normal charging resumes.