Xiaomi Poco X3 NFC BN57 Compatible Battery 3.85V 4950mAh

Xiaomi Poco X3 NFC — 3.85V Li-Polymer Replacement Battery (BN57)

This is a 3.85V, 4950mAh (19.06Wh) Li-Polymer cell for the Xiaomi Poco X3 NFC (M2007J20CG). It replaces OEM part BN57 directly. If your X3 NFC is shutting down early, holding minimal charge, or not turning on after sitting in a drawer, this is the cell to swap.

• Poco X3 NFC and M2007J20CG fit: Both model designations reference the same hardware platform — same 3.85V rail, same BN57 connector, same BMS handshake protocol. One cell covers both.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the X3 NFC platform. The BMS accepted the cell without fault flags, and the charge IC engaged fast charge on the second full cycle as expected.
• Fuel gauge recalibration on first use: Disable fast charging for the first complete discharge-charge cycle after installation. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes amps into an uncalibrated coulomb counter — preventing erratic percentage readings from the start.

Sudden shutdown at 20–30% on the Poco X3 NFC after a cell swap

This happens when the fuel gauge IC is still calibrated to the old cell's discharge curve. The X3 NFC's modem and 6.67-inch display draw sharp current spikes. A miscalibrated gauge reads 25% while the actual cell voltage has already dropped to the BMS cutoff threshold — roughly 3.2V — triggering an immediate shutdown. One full discharge-charge cycle without fast charging forces the coulomb counter to remap against the new cell. After that cycle, the reported percentage and actual cell state align.

USB-PD fast charge not activating on the first cycle after replacement

On the first charge cycle, the X3 NFC's charge IC runs a conditioning pass on the new cell — it defaults to standard 5V charging while it checks internal resistance and confirms BMS handshake. This is normal behaviour, not a fault. Fast charge typically re-engages from the second cycle onward. If it still does not activate after two full cycles, check that the cable and adapter support the phone's charging protocol, as the charge IC will fall back to standard current if the handshake fails at the adapter end.