Oppo BLP621 R9s Replacement Battery 3.85V 3000mAh

Oppo R9s / CPH1607 — 3.85V Li-Polymer Replacement Battery (BLP621)

This is a 3000mAh, 3.85V Li-Polymer cell built to the BLP621 specification for the Oppo R9s and R9s Dual SIM variants, including CPH1607. It fits the 2016 5.5-inch R9s lineup directly, restoring capacity when the original cell has degraded or failed. Install requires removing the rear cover and disconnecting the original flex connector.

• R9s and CPH1607 variant fit: The R9s, R9s Dual SIM, and R9s Dual SIM TD-LTE all share the same battery bay geometry, connector pinout, and BMS handshake protocol — which is why a single BLP621 cell covers the entire lineup without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on R9s hardware. The BMS accepted the cell, balancing terminated correctly at 4.35V, and protection cutoff triggered as expected at the low-voltage threshold.
• Fuel gauge recalibration on first use: On first use after installation, disable VOOC fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the R9s after a cell swap

This is a voltage-cliff failure, not a capacity problem. The fuel gauge IC is still referencing the discharge curve of the old, degraded cell. When the new cell hits a load spike — modem handoff, screen brightness jump, or GPS — the voltage briefly sags below the SoC estimate the IC is using, triggering an emergency shutdown. The fix is one full discharge-to-cutoff and charge-to-4.35V cycle without interruption. After that cycle, the coulomb counter recalibrates to the new cell's actual curve and the shutdowns stop.

VOOC fast charge not activating after BLP621 installation

Oppo's VOOC protocol requires a handshake between the charger adapter, the charge IC on the board, and the battery's internal BMS. On the first cycle after a cell swap, the BMS has not yet completed its initialisation sequence, so the charge IC defaults to standard 5V/1A input and VOOC never negotiates. Plug in the original Oppo VOOC adapter and let the first charge complete fully without unplugging mid-cycle. On the second charge, the VOOC handshake re-establishes and the adapter switches to high-current mode as normal.