Poco M4 5G Replacement Battery BN5H 3.87V 4900mAh

Poco M4 5G — 3.87V Li-Polymer Replacement Battery (BN5H)

This is a 3.87V, 4900mAh lithium-polymer replacement battery for the Poco M4 5G (MZB0BRZIN). It slots into the same position as the original BN5H cell and restores power to the display, processor, and 5G modem stack. Capacity is rated at 18.96Wh.

• M4 5G and MZB0BRZIN coverage: Both identifiers reference the same hardware revision — same battery bay dimensions (87.54 × 64.10 × 4.75mm), same connector pinout, and same BMS handshake expected by the MIUI charge IC. One cell fits both.
• Bench tested on actual hardware: We ran the BN5H replacement through charge and discharge cycles on the M4 5G board. The BMS accepted the cell without rejection flags, and the charge IC stepped through trickle, CC, and CV phases as expected on a healthy cell.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging in settings and run one full discharge-to-charge cycle at standard rate. This lets the coulomb counter recalibrate against the new cell's discharge curve before high-current fast charging is applied to an uncalibrated gauge.

Sudden shutdown at 20–30% on the Poco M4 5G

The M4 5G's 5G modem draws sharp current spikes during handoff and signal search. An aged or degraded cell cannot hold its voltage rail under that load, so the battery management system reads the voltage drop as a dead cell and forces shutdown — even when the OS fuel gauge still shows charge remaining. This is a voltage cliff, not a capacity issue. A fresh BN5H cell with lower internal resistance sustains the voltage rail through those modem spikes. After fitting the replacement, confirm the phone holds above 3.5V per cell under load by running one full discharge cycle before re-enabling 5G.

USB fast charge not accepted on the first cycle after fitting

On the first connection after a cell swap, MIUI's charge IC may refuse to negotiate the fast-charge protocol and fall back to standard 5W input. This happens because the charge controller checks BMS state before stepping up current, and a newly installed cell starts at an unverified state-of-charge. Plug into a standard charger — not a fast charger — and let the first cycle complete fully to 100% without interruption. After that cycle, the fast-charge handshake re-establishes at the expected rate.