MWG P3811 Replacement Battery 3.7V 1600mAh Li-Polymer

MWG P3811 / P3812 — 3.7V Li-Polymer Replacement Battery (WDSO080204873)

This 3.7V 1600mAh lithium-polymer cell replaces the original battery in the MWG P3811 and P3812 smartphones. It matches the OEM dimensions at 67.52 × 44.11 × 4.74mm and uses the same proprietary connector as the factory unit. Swap it when the original cell no longer holds a charge or causes unexpected shutdowns.

• P3811 and P3812 shared battery platform: Both handsets run the same 3.7V voltage rail, share the identical connector pinout, and use the same BMS handshake protocol — which is why a single cell covers both models without modification.
• Bench tested on actual hardware: We cycled this cell through full discharge and charge passes on the P3811 chassis. The BMS accepted charge correctly, protection cutoffs triggered at expected thresholds, and the fuel gauge IC tracked state of charge without error flags after the first full cycle.
• Fuel gauge recalibration on first use: After installing this cell, run one complete discharge-to-charge cycle with fast charging disabled. The phone's fuel gauge IC was calibrated to the old cell's discharge curve — giving it one clean cycle against the new cell lets it reset its reference points before high-current charging begins.

Why the P3811 reports wrong battery percentage after a cell swap

The P3811 uses a fuel gauge IC that builds a discharge model from accumulated cycle data on the original cell. When you install a fresh cell, that model no longer matches the new cell's actual voltage curve. The IC reads voltage and translates it to a percentage using the old curve, so it can report 40% when the real state of charge is closer to 60% — or vice versa. One full discharge from 100% down to automatic shutdown, followed by a full charge to 100%, forces the IC to rewrite its reference curve against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem, screen backlight, or both draw a current spike the cell cannot sustain at that state of charge — the cell voltage drops below the BMS protection threshold and the phone cuts off instantly. It is a voltage-sag problem, not a capacity problem. The BMS trips at approximately 3.0V per cell under load, even if the resting voltage reads higher. Let the phone reboot, charge it back to 100%, and complete that recalibration cycle — most users see this behaviour disappear after one or two full cycles.