Redmi Note 9 Pro BN5R Replacement Battery 3.82V 4900mAh

Redmi 23129RN51H / A3 4G — 3.82V Li-Polymer Replacement Battery (BN5R)

This is a 3.82V, 4900mAh (18.72Wh) Li-Polymer cell that replaces the original BN5R battery. It fits the Redmi Note 9 Pro variants 23129RN51H, 23129RN51X, and 2312CRNCCL, as well as the Redmi A3 4G. Use it when the original cell no longer holds charge through a normal day or swells and needs removal.

• Multi-variant fit — 23129RN51H, 23129RN51X, 2312CRNCCL, A3 4G: These models share the same BN5R footprint, connector pinout, and BMS handshake protocol, so one cell covers all four SKUs without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the 23129RN51H platform. The BMS accepted the cell without fault codes, and the charge IC stepped through trickle, CC, and CV phases correctly.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated state.

Why the Redmi A3 4G reports wrong battery percentage after a cell swap

The fuel gauge IC stores a learned discharge curve from the old cell in its coulomb counter memory. When a new cell goes in, the IC still references that old curve, so the percentage shown on screen drifts from actual cell state. The fix is one complete discharge from 100% down to automatic shutoff, followed by a full uninterrupted charge to 100% with fast charging off. After that single cycle, the IC resets its reference and percentage accuracy stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem locks onto a weak signal or the display brightness spikes — both draw enough current to pull the cell voltage below the BMS cutoff threshold before the percentage gauge catches up. A freshly installed cell with an uncalibrated fuel gauge makes this worse because the IC thinks there is more charge left than there is. Run the one full calibration cycle described above, then check that no background app is holding a wakelocked data connection during the first few days. If shutdown still occurs below 25%, check cell voltage under load — it should not drop below 3.4V at that state of charge.