Xiaomi Mix 4 BP43 Compatible Battery 7.74V 2200mAh

Xiaomi Mix 4 — 7.74V Li-Polymer Replacement Battery (BP43)

The BP43 is a 7.74V, 2200mAh Li-Polymer cell that fits the Xiaomi Mix 4 smartphone. It slots into the same footprint as the original at 88.40 × 64.50 × 5.70mm. Replace this battery when the original no longer holds charge through a normal day of use.

• Mix 4 fitment: The Mix 4 runs a dual-cell Li-Polymer pack at a nominal 7.74V rail. The BP43 matches that rail voltage and the board connector pinout, so the charge IC and fuel gauge IC receive the signals they expect without calibration errors at startup.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence on the Mix 4 board. The BMS accepted the cell on the first handshake, charge current ramped correctly through CC-CV stages, and no overvoltage flags were thrown at top-of-charge.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes significant current into an uncalibrated cell — preventing erratic percentage readings from the first charge onward.

Why the Mix 4 reports wrong battery percentage after a cell swap

The Mix 4 uses a coulomb counter-based fuel gauge IC that builds its capacity model from learned discharge data on the original cell. When you fit a new BP43, that learned model no longer matches the new cell's actual voltage-to-capacity curve. The gauge will show percentage values that do not reflect true remaining charge until it recalibrates. Run one full discharge down to automatic shutdown, then charge uninterrupted to 100% without fast charging active — that single cycle is usually enough for the IC to lock onto the new curve.

Sudden shutdown at 20–30% on the Mix 4 after replacement

This happens when the cell voltage drops below the BMS cutoff threshold under peak load — modem transmit bursts and display refresh pull current spikes the resting voltage reading does not predict. The fuel gauge shows 20–30% remaining, but instantaneous voltage sags below 3.0V per cell under that load spike. It is not a faulty battery; it is the gauge IC still working from an uncalibrated curve. Complete two full discharge-charge cycles without fast charging and the shutdowns typically stop once the IC's voltage model tightens up.