Poco X3 NFC Replacement Battery BN57 3.85V 4950mAh

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

This is a 3.85V, 4950mAh lithium-polymer replacement battery for the Poco X3 NFC (model M2007J20CG). It fits the original BN57 slot directly, matching the physical dimensions of 89.00 × 64.00 × 4.72mm. Capacity is rated at 19.06Wh, in line with the original cell specification.

• X3 NFC and M2007J20CG compatibility: Both model identifiers reference the same hardware platform. They share the same battery bay geometry, connector pinout, and BMS handshake protocol — one cell fits both.
• Bench tested on actual hardware: We ran this cell through a full charge cycle on an X3 NFC unit. The BMS accepted the charge handshake without fault flags, and the fuel gauge IC initialised correctly after one complete discharge-charge pass.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's discharge curve before Turbo Charge pushes high current into an uncalibrated cell.

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

This happens because the fuel gauge IC is still reading from the old cell's discharge curve. The new cell hits a voltage cliff — it cannot sustain rail voltage under simultaneous modem, display, and CPU load — even though the percentage shown looks safe. The phone's power management IC cuts the rail before the OS can log a proper shutdown. One full discharge-charge cycle with fast charging off forces the coulomb counter to rebuild its curve against the new cell and eliminates the false floor.

USB Turbo Charge not triggering after fitting a replacement BN57

Turbo Charge negotiation runs between the charger IC and the BMS on first contact. A new cell with a fresh BMS sometimes completes the initial handshake in standard 5V mode rather than elevated-voltage fast-charge mode. This typically resolves after the first full standard charge cycle, once the BMS has logged a complete charge event. If fast charging still does not trigger after two cycles, check that the cable supports the required current rating — a USB 2.0 data cable will cap current regardless of charger output.