WayteQ X620 Replacement Battery 3.7V 1200mAh Li-ion

WayteQ X620 — 3.7V Li-ion 1200mAh Replacement Battery

This is a 3.7V Li-ion cell rated at 1200mAh (4.44Wh), built to fit the WayteQ X620 smartphone. It replaces the original cell when the existing battery can no longer hold adequate charge across daily use cycles. Dimensions are 53.00 × 34.00 × 5.70mm — confirm these against your existing cell before installing.

• WayteQ X620 fitment: The X620 uses a compact removable cell on a 3.7V nominal rail. This cell matches that voltage rail and physical footprint, so the connector seats correctly and the charge IC communicates with the BMS without modification.
• Bench tested on actual hardware: We ran a full discharge-charge cycle and confirmed the BMS accepted charge input, reported state-of-charge to the OS, and terminated at the correct cutoff voltage without triggering a protection event.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This allows the fuel gauge IC to recalibrate its discharge curve against the new cell before high-current charging is applied to an uncalibrated cell.

Why the X620 reports wrong battery percentage after a cell swap

The X620's fuel gauge IC builds its state-of-charge model from the discharge curve of the original cell. When a new cell goes in, the IC is still referencing the old curve — so the percentage shown on screen does not match the actual charge level in the new cell. This mismatch is most visible as the battery appearing full but dropping quickly, or sitting at a fixed percentage for a long stretch. One full discharge down to auto-shutdown followed by a full uninterrupted charge resets the coulomb counter against the new cell's actual curve.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display draws a high current pulse and the cell voltage drops below the BMS protection threshold — even though the OS gauge still shows charge remaining. A fresh cell with an uncalibrated fuel gauge is especially prone to this because the reported percentage lags behind actual voltage. The BMS cuts power at roughly 3.0V per cell to prevent deep discharge damage. After one full calibration cycle, the OS percentage aligns more closely with real cell voltage and these unexpected cutoffs typically stop.