Xiaomi Mi 11 5G BM4X Replacement Battery 3.85V 4300mAh

Xiaomi Mi 11 5G — 3.85V Li-Polymer Replacement Battery (BM4X)

The BM4X is the OEM-matching lithium-polymer cell for the Xiaomi Mi 11 5G (M2011K2C, M2011K2G) and Mi 11T. It runs at 3.85V with a 4300mAh (16.56Wh) capacity. This cell replaces a degraded original when the phone can no longer hold a full charge or shuts down unexpectedly under load.

• Mi 11 5G and Mi 11T compatibility: Both models share the same BM4X cell, connector pinout, and BMS handshake protocol. The battery management IC communicates state-of-charge data over the same flex connector on both boards, so one cell covers all four variant SKUs listed above.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Mi 11 platform. The BMS accepted the cell without error codes, the fuel gauge IC initialized correctly, and charge current ramped as expected through CC/CV phases without tripping overcurrent protection.
• First-cycle fast charge hold-off: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before Xiaomi's high-current fast charging protocol pushes elevated current into an uncalibrated cell.

Why the Mi 11 shuts down at 20–30% after a cell swap

This is a voltage cliff problem, not a capacity problem. The fuel gauge IC is still running on the old cell's discharge curve stored in memory. When the new cell hits a voltage point that the old curve maps to 20–30%, the IC tells the OS the battery is critically low — even if actual charge remains. The phone cuts power to protect the modem and display from a voltage collapse that the IC falsely predicts is imminent. One full discharge to 0% followed by a complete charge cycle rewrites the coulomb counter reference and clears the false cliff.

USB-PD fast charge not triggering after replacement

On the first cycle after a cell swap, Xiaomi's charge IC sometimes refuses to enter fast charge mode because it cannot verify BMS state against its stored parameters. The phone charges slowly from a fast charger — not a charger fault or cable fault. Let the phone complete one full slow charge uninterrupted before attempting fast charge again. After that cycle the charge IC re-handshakes with the new BMS data and fast charge resumes at the rated current.