Oppo Reno 5K Replacement Battery BLP881 3.87V 4750mAh

Oppo Reno 5K / Reno K9 / Reno 4SE — 3.87V Li-Polymer Replacement Battery (BLP881)

This is a 3.87V, 4750mAh (18.38Wh) Li-Polymer cell built to the BLP881 specification. It fits the Oppo Reno 5K, Reno K9, and Reno 4SE. Install it when your original cell can no longer hold a charge through a normal day of use.

• Reno 5K, Reno K9, and Reno 4SE compatibility: All three models share the same physical footprint (94.00 × 65.10 × 4.35mm), the same 3.87V charge rail, and the same BMS handshake protocol — which is why one BLP881 cell covers the entire group.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Reno 5K unit. The BMS accepted the charge IC handshake cleanly, coulomb counter tracking initialised without error flags, and cell voltage held stable across the full discharge curve.
• First-cycle fast charge tip: On first use after installation, turn off fast charging and run one complete discharge-charge cycle at standard rate. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current fast charging pushes significant current into an uncalibrated cell.

Sudden shutdown at 20–30% on the BLP881 replacement cell

This happens because the fuel gauge IC is still running the discharge curve it learned from the old, degraded cell. When the new cell hits a voltage point the IC hasn't mapped correctly, it reads the state-of-charge as critical and triggers a protective shutdown — even though real capacity remains. The fix is one full discharge-to-shutdown followed by an uninterrupted charge to 100%, which forces the coulomb counter to recalibrate its endpoints against the new cell. After two or three of these full cycles, the percentage readout stabilises and the premature shutdowns stop.

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

The Reno 5K uses Oppo's VOOC charge protocol, which requires the charge IC and BMS to complete a handshake before high-current delivery begins. On a freshly installed cell, the BMS occasionally does not complete this handshake on the first connection — so the phone falls back to standard 5V charging instead. Disconnect the cable, power the phone off fully, then reconnect. If fast charging still does not activate, complete one standard charge cycle first; the BMS handshake typically succeeds on the second cycle once the cell voltage is above 3.7V.