W77 Replacement Battery 3.7V 1200mAh Li-ion for Amico Smartphone

Amico W77 — 3.7V Li-ion 1200mAh Replacement Battery (W77)

This is a 3.7V 1200mAh Li-ion cell from the Amico X-Longer series, replacing part number W77. It fits smartphones that originally shipped with the W77 cell. Capacity is 1200mAh (4.44Wh) — matching the original specification.

• W77 cell platform: Devices using the W77 share a common connector pinout and BMS handshake voltage threshold. The replacement cell matches the original discharge curve so the fuel gauge IC has a consistent reference point from the first cycle.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a W77-compatible board, monitoring BMS cutoff at both ends. The protection circuit tripped correctly at low voltage and released cleanly on reconnection to a charger — no latching faults observed.
• First-cycle calibration tip: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.

Why the phone reports wrong battery percentage after a cell swap

The fuel gauge IC builds its percentage model from the old cell's discharge curve stored in its coulomb counter. When a new cell goes in, that learned curve no longer matches the actual voltage-to-capacity relationship. The phone reads voltage, compares it to the old map, and outputs a percentage that is off — sometimes by 15–20 points. One full discharge down to automatic shutdown, followed by a full charge to 100%, forces the IC to rebuild its curve against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the modem or display load threshold before the fuel gauge reaches 0%. A fresh cell with an uncalibrated IC shows 25% on screen while actual cell voltage has already fallen to roughly 3.4V under load. The BMS cuts power to protect the cell, and the phone shuts down without warning. Run one full calibration cycle — discharge to auto-shutdown, charge uninterrupted to 100% — and the IC will map the voltage cliff correctly so the shutdown warning fires at the right level.