Redmi BN5K 11A Replacement Battery 3.82V 4900mAh

Redmi 11A / 12C Series — 3.82V Li-Polymer Replacement Battery (BN5K)

This is a 3.82V, 4900mAh Li-Polymer replacement battery for the Redmi 11A and 12C smartphones, using OEM part number BN5K. It fits models 22120RN86C and 22120RN86G among others in that lineup. Swap it when the original cell no longer holds charge or causes unexpected shutdowns during normal use.

• 11A and 12C platform fit: Both phones share the same battery bay dimensions and BMS connector pinout, which is why one BN5K cell covers the full model range. The charge IC on both boards negotiates with the same BMS handshake, so no firmware mismatch occurs at the cell level.
• Bench tested on actual hardware: We cycled this cell through full charge and load discharge on a Redmi 11A board. The BMS accepted the cell on first connection, protection cutoffs triggered correctly at low voltage, and the charge IC held a stable termination current at end-of-charge.
• Fuel gauge recalibration on first use: After installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This gives the fuel gauge IC a clean reference discharge curve for the new cell before high-current fast charging pushes load into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on the Redmi 11A after a cell swap

This happens because the fuel gauge IC still holds the discharge curve of the old degraded cell. When the new cell hits a voltage point that the old curve mapped to 20–30%, the IC signals a low-voltage event and the board cuts power. The fix is one full uninterrupted discharge down to automatic shutdown, followed by a full charge without interruption. After that single cycle the coulomb counter resets against the actual capacity of the new 4900mAh cell.

Turbo or fast charge not activating after BN5K installation

On the first charge cycle after installation, the charge IC on the Redmi 11A board may refuse to step up to high-current mode because the BMS in the new cell has not yet confirmed thermal and impedance status to the host. This is a deliberate first-cycle safety hold, not a fault with the cell. Plug in using the original cable and charger and let the first charge complete fully at standard rate — the IC will log the handshake and fast charge will activate from the second cycle onward. If it still does not activate, check that the USB-C port is clean and the charger outputs at least 9V 2A.