About this replacement
Xiaomi Mi 4 Series — 3.8V Li-Polymer Replacement Battery (BM32)
This is a 3.8V, 3000mAh lithium-polymer cell for the Xiaomi Mi 4, Mi 4 4G, and Mi 4W smartphones. It replaces part number BM32 when the original cell has degraded or failed to hold charge. Capacity is rated at 11.4Wh and dimensions are 65.90 × 55.72 × 5.23mm — a direct physical match to the stock battery bay.
- Mi 4 platform compatibility: The Mi 4, Mi 4 4G, and Mi 4W share the same battery bay dimensions and BM32 connector pinout. The BMS communication line on each variant runs on the same protocol, so one cell covers all three without wiring changes.
- Bench tested on actual hardware: We ran this cell on the Mi 4 mainboard and confirmed the BMS handshake completed correctly — charge IC accepted the cell, fuel gauge IC began tracking, and thermal monitoring remained active throughout the charge cycle.
- First-cycle fast charge caution: On first use after installation, disable fast charging for one full discharge-charge cycle. This gives the Mi 4's fuel gauge IC time to recalibrate against the new cell's discharge curve before high-current charging pushes into an uncalibrated state.
Why the Mi 4 reports wrong battery percentage after a cell swap
The Mi 4 uses a coulomb counter in the fuel gauge IC that builds its model from the old cell's charge-discharge history. When you install a new cell, that learned model no longer matches the actual discharge curve. The IC keeps reading from its old reference, so the percentage shown on screen drifts from reality — often reading 100% until a sudden drop. One complete discharge down to automatic shutdown, followed by a full uninterrupted charge to 100%, forces the IC to write a new baseline against the replacement cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage collapses under load before the displayed percentage reaches zero. On the Mi 4, simultaneous LTE modem activity and screen-on draw can pull enough current to expose a voltage sag the fuel gauge IC did not anticipate. The IC sees the terminal voltage drop below the shutdown threshold — typically around 3.2V — and cuts power immediately, even though the percentage indicator still showed capacity remaining. Running the full calibration cycle described above reduces this by anchoring the IC's low-voltage reference to the actual knee of the new cell's discharge curve.