Xiaomi Mi Mix 2 BM3B Replacement Battery 3.85V 3000mAh

Xiaomi Mi Mix 2 — 3.85V Li-Polymer Replacement Battery (BM3B)

This is a 3000mAh, 3.85V Li-Polymer replacement cell for the Xiaomi Mi Mix 2 smartphone. It fits the Mix 2, MDE5, Mi Mix 2S, and Mi Mix 2S Standard Edition Global, along with additional variant models. Swap this in when the original BM3B cell no longer holds a full day's charge or refuses to charge past a certain percentage.

• Mix 2 and Mix 2S platform fit: Xiaomi shared the BM3B cell across the Mix 2 and Mix 2S lines because both use the same 3.85V rail, identical connector pinout, and compatible BMS handshake with the PMIC on that platform. One cell covers both boards.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Mix 2 board. The BMS accepted the cell without fault flags, and the charge IC stepped through trickle, CC, and CV phases cleanly at rated current.
• First-cycle fast charge disable on Mi Mix 2S: On first use after installation, turn off Mi Turbo Charge for one full discharge-charge cycle. The fuel gauge IC is still calibrated to the old cell curve — running fast charge into an uncalibrated cell causes the coulomb counter to log inaccurate state-of-charge data that compounds over subsequent cycles.

Why the Mi Mix 2 reports wrong battery percentage after a cell swap

The fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, the IC still references that old curve, so the percentage shown on screen drifts from the real state of charge. The fix is one full uninterrupted discharge down to automatic shutdown, followed by a complete charge to 100% without interruption. After that cycle, the coulomb counter resets its reference points against the new cell and percentage accuracy stabilises.

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%. The new Li-Polymer cell has a steeper voltage cliff than a degraded original cell, so the PMIC cuts power while the OS still shows charge remaining. Run one full calibration cycle first — discharge to shutdown, charge uninterrupted to 100%. If shutdowns continue, check that the replacement cell rests at or above 3.7V open-circuit before installation.