Xiaomi Redmi Note 11 Pro BM5A Replacement Battery 3.87V 4900mAh

Xiaomi Redmi Note 11 Pro — 3.87V Li-Polymer Replacement Battery (BM5A)

This is a 3.87V, 4900mAh (18.96Wh) Li-Polymer cell replacing the OEM BM5A battery. It fits the Redmi Note 11 Pro (21091116C) and Note 11i 5G (21091116I). Install it when the original cell no longer holds a charge or the phone shuts down unexpectedly under load.

• Redmi Note 11 Pro and Note 11i 5G fit: Both the 21091116C and 21091116I variants share the same BM5A form factor, connector pinout, and NTC thermistor line. The BMS handshake on these models uses the same authentication sequence, so the replacement cell is recognised at first boot without error codes.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Redmi Note 11 Pro unit. The BMS accepted the cell, fast-charge handshake completed on the second cycle, and the protection circuit tripped correctly at the low-voltage cutoff threshold without hard-crashing the OS.
• First-cycle calibration tip: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC build an accurate discharge curve against the new cell before high-current fast charging pushes current into an uncalibrated coulomb counter.

Why the Redmi Note 11 Pro shuts down suddenly at 20–30% after a cell swap

The fuel gauge IC stores a discharge curve calibrated to the original cell. A new cell with a different internal resistance profile hits a voltage cliff at a different state of charge than the IC expects. Under modem or display load, the cell voltage drops sharply, the BMS trips the low-voltage cutoff, and the phone powers off even though the gauge still shows 20–30%. One full uninterrupted discharge-to-shutdown followed by a complete charge resets the coulomb counter against the new cell's actual curve. After that cycle, the reported percentage tracks real capacity accurately.

USB-PD fast charge not accepted on first cycle after replacement

Some BM5A replacement cells present a slightly elevated impedance on the first charge because the electrolyte has not yet fully wetted the electrode stack. The charge IC reads this impedance, interprets it as an out-of-spec condition, and drops back to standard 5V charging rather than negotiating the higher-voltage fast-charge profile. Charge the phone once at standard rate until full, then fast charging typically resumes normally on the next session. If it does not resume after two standard-rate cycles, check that the cable and adapter are rated for the phone's fast-charge protocol — the handshake starts at the adapter end, not the battery.