Redmi Note 9T BM54 Compatible Battery 3.85V 4900mAh

Redmi Note 9T / Note 9 5G — 3.85V Li-Polymer Replacement Battery (BM54)

The BM54 is a 3.85V 4900mAh lithium-polymer cell that fits the Redmi Note 9T, Note 9 5G, A001XM, and M2007J22R. It replaces a degraded or swollen original cell in this mid-range Android smartphone. At 18.87Wh, it matches the factory capacity specification exactly.

• Note 9T / Note 9 5G platform fit: Both models share the same physical envelope, connector pinout, and BMS handshake protocol, which is why one cell covers the full variant list. The power management IC accepts the same voltage rail and charge termination signals across all listed model numbers.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Note 9T platform. The BMS accepted charge termination at 4.35V without error flags, and the coulomb counter tracked state-of-charge correctly after one full cycle.
• Fuel gauge recalibration on first use: 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 charging pushes into an uncalibrated state-of-charge register.

Sudden shutdown at 20–30% on the BM54 replacement cell

This is a voltage cliff issue, not a capacity defect. Under high-load conditions — active 5G modem, screen at full brightness, background sync — the cell voltage drops faster than the fuel gauge IC predicts. When voltage sags below the protection threshold, the BMS trips and cuts power even though the percentage display still shows charge remaining. One full discharge-charge cycle recalibrates the coulomb counter and closes the gap between the displayed percentage and actual cell voltage.

USB-PD fast charge not activating on the first cycle after replacement

On the first charge after a cell swap, the charge IC may not negotiate the fast charge protocol correctly. The BMS on a new, uncalibrated cell defaults to a conservative current limit until the fuel gauge IC has a baseline curve to work from. Plug in with the original cable and charger, let the phone complete a full slow charge to 100%, then allow it to discharge to under 10% before charging again. After that cycle, fast charging typically resumes at the rated current.