Xiaomi Redmi Note 7 BN4A Replacement Battery 3.85V 3900mAh

Xiaomi Redmi Note 7 — 3.85V Li-Polymer Replacement Battery (BN4A)

This is a 3.85V, 3900mAh Li-Polymer cell built to the BN4A specification. It fits the Redmi Note 7, including variants M1901F7G, M1901F7H, and M1901F7C. If your original battery swells, drains rapidly, or shuts down unexpectedly, this cell restores full capacity to the handset.

• M1901F variant coverage: The Note 7 shipped across multiple regional variants — M1901F7G (Global), M1901F7H (India), and M1901F7C (China) among others. All share the same BN4A cell footprint, connector, and BMS handshake, so one replacement covers the full production run.
• Bench tested on actual hardware: We cycled this cell through charge and load on the Redmi Note 7 platform. The BMS accepted the charge IC handshake without error flags, and the coulomb counter tracked state-of-charge across the full voltage window from 4.35V down to 3.0V cutoff.
• Fuel gauge recalibration after installation: On first use after fitting, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

This happens because the fuel gauge IC is still using the discharge curve learned from the degraded original cell. The new cell has a steeper voltage drop under load — modem transmit bursts and AMOLED peaks pull several hundred milliamps simultaneously. The PMIC reads a voltage sag and trips the low-battery cutoff before the percentage display reflects actual remaining capacity. One full slow-charge cycle forces the coulomb counter to relearn the curve, and the shutdowns stop.

USB fast charge not working on first cycle after fitting the BN4A

Xiaomi's proprietary fast charge protocol requires a BMS handshake between the charge IC and the cell's protection circuit. On a new cell, the BMS starts in a conservative state and may not complete that handshake on the first charge attempt. Plug in via standard 5V before using the bundled fast charger. Once the cell reaches a full charge at standard rate, the BMS unlocks the higher-current pathway and fast charging resumes normally on subsequent cycles.