Xiaomi Mi 5c Replacement Battery BN20 3.85V 2850mAh

Xiaomi Mi 5c — 3.85V Li-Polymer Replacement Battery (BN20)

The BN20 is a 3.85V Li-Polymer cell rated at 2850mAh (10.97Wh), made to fit the Xiaomi Mi 5c and Mi 5c Dual SIM TD-LTE. It restores power to a phone that drains too fast, won't hold charge, or won't turn on. Install it when the original cell has degraded past the point of normal daily use.

• Mi 5c and Meri compatibility: All three listed variants — Mi 5c, Mi 5c Dual SIM TD-LTE, and Meri — use the same BN20 footprint, connector pinout, and BMS handshake. The voltage rail and NTC thermistor wiring are shared across the range, so one cell fits all three.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Mi 5c unit. The BMS accepted charge handshake without fault. Voltage held steady above 3.6V through normal load draws including screen-on and cellular activity.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one full discharge down to automatic power-off, then charge to 100% on standard current. This lets the phone's fuel gauge IC map its coulomb counter to the new cell's actual discharge curve before fast charge current is applied to an uncalibrated state.

Sudden shutdown at 20–30% on the Mi 5c after a cell swap

This happens because the fuel gauge IC is still running a lookup table calibrated to the old, degraded cell. The new cell has a steeper voltage drop under modem and display load than the IC expects at that state of charge. The phone interprets the voltage sag as an empty cell and cuts power. One full discharge-to-shutdown cycle followed by a full charge resets the coulomb counter and eliminates the false cutoff. After that cycle, shutdowns below 20% should stop.

Phone won't power on after the BN20 sat in storage

Li-Polymer cells self-discharge in storage. If the BN20 dropped below approximately 2.5V per cell, the BMS will have entered lockout mode to prevent damage — the phone will show no response to the power button. Connect the phone to a wall adapter, not a USB port, and leave it for 15–20 minutes without pressing anything. The charge IC needs enough current to bring the cell above the BMS recovery threshold, typically around 3.0V, before the power rail re-enables. Once the screen shows a charging indicator, normal startup will proceed.