Redmi 12 5G BM5R Replacement Battery 3.87V 5000mAh

Redmi 12 5G — 3.87V Li-Polymer Replacement Battery (BM5R)

This is a 3.87V, 5000mAh Li-Polymer battery carrying OEM part number BM5R. It fits the Redmi 12 5G smartphone. It replaces the original cell when the phone no longer holds a full charge, shuts down unexpectedly, or fails to power on.

• Redmi 12 5G fit: The BM5R uses the same connector pinout and physical footprint as the factory cell. The BMS communicates over the same data line the phone's charge IC expects, so the system accepts the cell without hardware modification.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the Redmi 12 5G. The BMS reported correct voltage thresholds at both ends of the curve, and the charge IC accepted USB-PD input without rejecting the session.
• First-cycle fast charging: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the phone's fuel gauge IC build an accurate discharge curve against the new cell before high-current fast charging pushes elevated current into an uncalibrated state.

Sudden shutdown at 20–30% on the Redmi 12 5G

This happens when the fuel gauge IC is still calibrated to the old cell's discharge curve. The phone reads 25% but the actual cell voltage has already dropped below what the modem and display need under load. The BMS triggers a protection cutoff before the OS gets a low-battery warning. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the coulomb counter to reset against the new cell's actual curve.

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

After a cell swap, the charge IC sometimes declines the fast-charge handshake on the first session because the BMS on the new cell has not yet passed a full authentication cycle with the phone's PMIC. This is not a fault with the battery or the charger. Charge once at standard 5W, let the cycle complete fully, then reconnect the fast charger. The handshake succeeds reliably from the second cycle onward.