Motorola HX40 Moto X4 Replacement Battery 3.8V 2800mAh

Motorola Moto X4 — 3.8V Li-Polymer Replacement Battery (HX40 / SNN5995A)

This is a 3.8V, 2800mAh Li-Polymer replacement battery for the Motorola Moto X4, Moto X4 LTE-A LATAM, and variants including XT1900-1 and XT1900-4. It replaces OEM part numbers HX40 and SNN5995A. Install it when the original cell has degraded past the point of holding usable charge through a normal day.

• XT1900 series compatibility: All XT1900 variants share the same battery bay dimensions, connector pinout, and BMS communication protocol. The fuel gauge IC on each variant reads the same cell chemistry, so one cell fits the full range without hardware modification.
• Bench tested on actual hardware: We ran this cell on an XT1900-4 and monitored the BMS handshake through three full charge cycles. The charge IC accepted the new cell on the first cycle, and the BMS cutoff triggered correctly at the low-voltage threshold without spurious shutdowns.
• Fuel gauge recalibration on first use: Disable fast charging for the first complete discharge-charge cycle after installation. The fuel gauge IC on the Moto X4 calibrates its coulomb counter against the new cell's discharge curve. Running fast charge before that calibration completes can push current into an uncalibrated cell and produce inaccurate percentage readings from the start.

Sudden shutdown at 20–30% on the Moto X4 after a cell swap

This happens because the fuel gauge IC is still reading the discharge curve of the old, degraded cell. When the new cell hits a voltage point the IC hasn't mapped yet, it misreads remaining capacity and cuts power before the battery is actually empty. The phone sees a voltage drop under modem or screen load and interprets it as a dead cell. One full discharge-charge cycle — taken to under 5% and charged to 100% without interruption — lets the coulomb counter remap the curve and eliminates most premature shutdowns.

USB-PD fast charge not activating on the first cycle after replacement

On the first charge cycle, the Moto X4's charge IC may not negotiate the fast-charge protocol with the new cell's BMS until the cell has passed through at least one standard charge. This is a BMS initialisation behaviour, not a hardware fault. Use a standard 5V charger for the first full cycle. After that cycle completes, fast charging via the original Motorola TurboPower adapter should negotiate correctly at the expected voltage step.