BLP689 Oppo R15x Replacement Battery 3.85V 3400mAh

Oppo R15x / PBCT10 / PBCM10 — 3.85V Li-Polymer Replacement Battery (BLP689)

This is a 3400mAh 3.85V Li-Polymer replacement cell for the Oppo R15x, R15x Dual SIM, PBCT10, and PBCM10 smartphones. It replaces the original BLP689 cell when capacity has dropped to the point where the phone no longer gets through a full day. Rated at 13.09Wh, it matches the original voltage and physical footprint exactly.

• R15x / PBCT10 / PBCM10 platform fit: All four variants — R15x, R15x Dual SIM, PBCT10, and PBCM10 — share the same battery bay dimensions, connector pinout, and BMS communication protocol, which is why a single BLP689 cell covers the entire lineup without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the R15x platform. The BMS handshake completed correctly, the charge IC accepted the cell without fault codes, and the fuel gauge IC tracked state-of-charge across the full voltage window from 4.35V down to 3.0V.
• First-cycle fast charge protocol: On first use after installation, disable VOOC fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current pulses are introduced into an uncalibrated cell.

Why the R15x reports wrong battery percentage after a cell swap

The R15x uses a coulomb-counting fuel gauge IC that tracks charge by measuring current flow in and out of the original cell over time. When a new cell goes in, the IC's stored discharge curve no longer matches the actual chemistry of the new cell. The percentage reading drifts — often showing full charge when the cell is at 80%, or dropping sharply near the end. One full discharge down to auto-shutdown followed by a complete charge to 100% forces the IC to rebuild its reference curve against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC has not yet recalibrated after the swap. At 20–30% as reported by the uncalibrated counter, the actual cell voltage may already be at or below 3.5V under modem and display load — enough for the hardware voltage monitor to trigger an emergency shutdown before the OS can react. It is not a faulty cell. Run one full discharge-charge cycle without fast charging, let the phone shut itself off naturally at the bottom, then charge uninterrupted to 100%. After that cycle the shutdown threshold aligns with the actual cell voltage.