About this replacement
Poco F4 5G — 3.87V Li-Polymer Replacement Battery (BP49)
This 3.87V, 4400mAh (17.03Wh) Li-Polymer battery replaces the BP49 cell in the Poco F4 5G smartphone. It fits model variants 22021211RG and 22021211RI. Capacity figure is taken directly from product data — not extrapolated from any third-party source.
- F4 5G variant coverage: The 22021211RG and 22021211RI model codes share the same BP49 footprint, connector pinout, and BMS handshake protocol. Both accept this cell without physical or electrical modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on F4 5G hardware. The BMS accepted charge current correctly, voltage hold under display and modem load stayed stable, and the protection circuit tripped at the expected low-voltage threshold.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter to the new cell's discharge curve before high-current charging begins on an uncalibrated reference.
Sudden shutdown at 20–30% on the replacement cell
The F4 5G's fuel gauge IC carries the calibration data from the original cell. After a swap, its voltage-to-percentage curve no longer matches the new cell's actual discharge profile. Under heavy load — 5G modem active, screen at full brightness — the cell voltage drops faster than the IC predicts, crossing the hardware cutoff before the displayed percentage reaches zero. Run one full discharge cycle without fast charging to force the IC to recalibrate against the new cell. After that cycle, the shutdown threshold should align to a percentage below 10%.
USB-PD fast charge not triggering on the first cycle after swap
Some replacement cells ship with the BMS in a conservative initialisation state. On the first charge cycle, the BMS may not complete the handshake required for the F4 5G's fast-charge protocol, so the charger falls back to standard 5V output. This is not a fault with the charger or the port. Allow the first cycle to complete at standard rate — once the BMS logs a full charge-discharge event, it exits the initialisation state and fast charge negotiation resumes normally on the next plug-in.