Xiaomi Mi 5s BM36 Replacement Battery 3.85V 3100mAh

Xiaomi Mi 5s Series — 3.85V Li-Polymer Replacement Battery (BM36)

This is a 3.85V, 3100mAh (11.94Wh) Li-Polymer replacement battery for the Xiaomi Mi 5s, Mi 5s Premium Edition, Mi 5s Extreme Edition, and Mi 5s Extreme Edition Dual SIM. It uses OEM part number BM36 and fits the same battery bay with the same connector orientation. Capacity listed here comes from product data — not web estimates.

• Mi 5s variant compatibility: All four listed models — standard, Premium Edition, Extreme Edition, and Extreme Edition Dual SIM — share the same BM36 form factor, connector pinout, and 3.85V nominal voltage rail. No hardware differences between variants affect battery fitment.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the Mi 5s platform. The BMS handshake completed without error codes, charge termination triggered at the correct cutoff voltage, and protection circuits responded normally to load fluctuations from the modem and display.
• First-cycle fast charge protocol: On first use after installation, disable fast charging for one complete discharge-charge cycle. The fuel gauge IC calibrates its coulomb counter against the new cell's discharge curve. Running fast charge into an uncalibrated cell can push current at the wrong rate before the IC has an accurate baseline.

Why the Mi 5s reports wrong battery percentage after a cell swap

The fuel gauge IC stores a discharge curve profile learned from the original cell. When a new BM36 cell goes in, that stored curve no longer matches the actual cell chemistry and impedance. The percentage reading drifts — sometimes reading 40% while the phone is close to cutoff voltage. One full discharge down to automatic shutdown, followed by an uninterrupted charge to 100%, forces the IC to rewrite its reference curve against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the system's minimum threshold under high instantaneous load — typically a 4G modem transmission burst or screen brightness spike — even though the reported percentage looks safe. A fresh Li-Polymer cell has slightly different internal resistance than the original, and the fuel gauge IC has not yet mapped where the voltage cliff sits on this cell. Run two full cycles without fast charging to let the coulomb counter recalibrate. After recalibration, the OS will report shutdown risk closer to the actual voltage floor of 3.0V per cell.