OPPO Reno 11 Replacement Battery BLPA31 3.91V 4800mAh

Oppo Reno 11 / CPH2599 — 3.91V Li-Polymer Replacement Battery (BLPA31)

The BLPA31 is the OEM-referenced Li-Polymer cell for the Oppo Reno 11, Reno 11 5G, and CPH2599. It runs at 3.91V nominal with 4800mAh (18.77Wh) capacity. This replaces a degraded original cell that can no longer hold a full charge after repeated charge cycles.

• Reno 11 / Reno 11 5G / CPH2599 fit: All three share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The BLPA31 part number maps directly to this hardware revision — no adapter or rewiring needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Reno 11 platform. The BMS accepted the cell without fault codes, fast-charge negotiation completed normally after the first full cycle, and the fuel gauge IC tracked state-of-charge without erratic jumps.
• First-cycle fuel gauge recalibration: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This gives the fuel gauge IC a clean reference curve for the new cell before high-current charging loads are applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

A new cell has a different voltage-discharge curve than the worn cell the fuel gauge IC was calibrated against. When the phone hits a load spike — 5G modem handoff, screen-on burst, or background sync — the cell voltage drops below the protection threshold faster than the gauge expects. The OS reads 25% remaining but the actual cell voltage has already collapsed under load. One full discharge-charge cycle at standard rate forces the coulomb counter to remap against the new cell's curve, and shutdowns at partial charge typically stop after that.

USB-PD fast charge not working on first cycle after replacement

The Reno 11 charge IC runs a handshake check on the first charge session after a new cell is detected — it measures internal resistance and validates BMS response before enabling the full fast-charge current profile. On a cold or unconditioned cell, this check can cause the phone to fall back to standard 5W charging. Letting the phone complete one full charge at standard rate resolves the handshake state. After that cycle, fast charging re-enables at the expected wattage — confirmed at 3.91V open-circuit on our bench unit before reinstallation.