About this replacement
Redmi Note 12 4G — 3.87V Li-Polymer Replacement Battery (BN5M)
This is a 3.87V, 4900mAh Li-Polymer replacement battery for the Xiaomi Redmi Note 12 4G smartphone. It carries OEM part number BN5M and fits models 23028RA60L, Note 12 4G NFC (23021RAA2Y), and related variants. Install it when the original cell no longer holds charge through a normal day or shuts down unexpectedly under load.
- Note 12 4G variant coverage: The 23028RA60L and 23021RAA2Y share the same battery bay dimensions, connector pinout, and BMS handshake protocol — one cell fits all listed variants without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Note 12 4G platform. The BMS accepted the USB-PD and Xiaomi 33W fast charge handshake cleanly after the first complete 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 map the new cell's discharge curve before high-current charging pushes into an uncalibrated state.
Sudden shutdown at 20–30% on the Note 12 4G after a cell swap
A new Li-Polymer cell has a slightly different internal resistance profile than the worn cell the fuel gauge IC learned against. Under modem or display load, the new cell's voltage drops faster than the IC predicts, triggering a low-voltage cutoff well above the displayed percentage. The phone reads 25% but the cell voltage has already fallen below 3.5V at high draw. One full discharge-charge cycle with fast charging disabled corrects the coulomb counter and the shutdowns stop.
OS reports wrong battery percentage after replacement
The fuel gauge IC on the Note 12 4G stores a learned discharge curve from the original cell. A replacement cell with a different impedance curve makes those stored values inaccurate from the first boot. The percentage readout can jump, stall, or read 100% well before the cell is full. Run one full uninterrupted discharge down to auto-shutdown, then charge to 100% without interruption — this forces the IC to rewrite its reference curve against the new cell.