Oppo Realme 5 Pro BLP731 Compatible Battery 3.85V 3900mAh

Oppo Realme 5 Pro / RMX1971 — 3.85V Li-Polymer Replacement Battery (BLP731)

This is a 3.85V, 3900mAh (15.02Wh) Li-Polymer cell built to the BLP731 specification for the Realme 5 Pro (RMX1971). It replaces the original battery when capacity fade makes the phone unreliable through a normal day. Voltage, connector, and BMS communication match the factory cell.

• Realme 5 Pro / RMX1971 fitment: Both model designations share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The BLP731 cell covers both — no adapter or modification needed.
• Bench tested on actual hardware: We ran the BLP731 through charge and discharge cycles on the RMX1971 board. The BMS accepted the cell without fault flags, and the charge IC stepped through VOOC pre-charge, CC, and CV phases as expected.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-charge cycle on standard 5W. This gives the fuel gauge IC one complete sweep of the new cell's discharge curve before high-current VOOC charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the Realme 5 Pro after a cell swap

The Realme 5 Pro's fuel gauge IC holds a discharge curve from the original cell in its coulomb counter. When a new cell goes in, the stored curve no longer matches the actual voltage drop profile of the fresh Li-Polymer cell. Under peak load — modem transmit or screen at full brightness — the phone hits a voltage point it incorrectly reads as critically low and shuts down, even with usable capacity remaining. One full discharge to automatic power-off, followed by a complete charge to 100%, resets the coulomb counter against the new cell. After that cycle, the percentage reporting stabilises.

VOOC fast charge not activating after BLP731 installation

Realme's VOOC protocol requires a handshake between the charger, the charge IC on the board, and the battery BMS before elevated current is allowed. On the first cycle with a new cell, the BMS may not complete that handshake, so the phone falls back to standard 5W charging. This is not a fault — it clears after one standard charge cycle at 5V/1A. If VOOC still does not activate on the second cycle, check that the original VOOC adapter is in use, since third-party chargers do not carry the protocol regardless of cable quality.