BN43 Xiaomi Redmi Note 4X Compatible Battery 3.85V 4000mAh

Xiaomi Redmi Note 4X China Version — 3.85V Li-Polymer Replacement Battery (BN43)

This is a 3.85V, 4000mAh Li-Polymer replacement cell for the Xiaomi Redmi Note 4X China Version. It replaces OEM part BN43, which sits behind the rear panel on this model. Voltage and capacity match the original spec to keep the charge IC and fuel gauge IC operating within their calibrated ranges.

• Redmi Note 4X China Version fit: This battery fits the China-market Redmi Note 4X specifically. That variant uses the BN43 cell and a Snapdragon 625 platform. The global Note 4X uses a different board layout and a different OEM battery — confirm your model before ordering.
• Bench tested on actual hardware: We ran the BN43 replacement through a full charge cycle on a Redmi Note 4X China unit. The charge IC accepted the cell without error, BMS protection tripped correctly at the low-voltage cutoff threshold, and the fuel gauge IC began tracking state-of-charge within the first cycle.
• Fuel gauge recalibration on first use: After installation, disable fast charging and run one complete discharge-to-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before fast charging pushes higher current into an uncalibrated cell. Skip this step and percentage readouts will drift for several days.

Why the Redmi Note 4X reports wrong battery percentage after a cell swap

The fuel gauge IC on the Redmi Note 4X uses a coulomb counter that was calibrated to the original BN43 cell's internal resistance and discharge curve. A new cell has lower impedance, so the counter's learned model no longer matches actual cell behaviour. The result is percentage jumps, early low-battery warnings, or the bar sitting at 100% longer than expected. One full discharge below 5% followed by a full charge at standard rate resets the learned curve and brings readouts back to accuracy.

Sudden shutdown at 20–25% on the replacement cell

This happens when the modem, display, or both pull a current spike the cell cannot sustain while holding voltage above the shutdown threshold. Aged cells hit this cliff earlier, but a new cell can show the same fault if the fuel gauge IC is still running an old calibration. The phone's PMIC reads a voltage drop below approximately 3.4V and cuts power before the OS can react. Run one full calibration cycle first — if shutdowns persist past that point, check that no third-party app is preventing a clean full discharge.