About this replacement
Oppo Realme Q3s / Narzo 50 — 3.87V Li-Polymer Replacement Battery (BLP875)
The BLP875 is a 4800mAh Li-Polymer cell at 3.87V, direct replacement for the Realme Q3s, Realme Narzo 50, and RMX3286. It restores full power delivery to the processor, display, and modem after the original cell degrades. Capacity is 18.58Wh — matched to the original specification.
- Q3s, Narzo 50, and RMX3286 compatibility: These three models share the same PCB footprint, connector pinout, and BMS handshake protocol. The BLP875 cell dimensions — 94.50 × 65.10 × 4.30mm — fit the battery bay on all three without modification.
- Bench tested on actual hardware: We ran the BLP875 through charge and discharge cycles on an RMX3286 unit. The BMS accepted the cell without fault flags, and the fuel gauge IC registered correct capacity across the full voltage range from 4.4V to cutoff.
- First-cycle fast charge protocol: On first use after installation, disable fast charging and complete one full discharge-charge cycle at standard rate. This allows the fuel gauge IC to recalibrate its coulomb counter against the new cell's discharge curve before high-current charging is applied to an uncalibrated cell.
Why the Realme Q3s reports wrong battery percentage after a cell swap
The fuel gauge IC on the Q3s uses a coulomb counter that was calibrated to the discharge curve of the original cell. When a new cell goes in, that learned curve no longer matches reality. The IC will report incorrect percentages — sometimes high, sometimes dropping suddenly — until it recalibrates. One complete discharge from 100% to auto-shutdown, followed by a full uninterrupted charge, resets the counter to the new cell's actual curve.
Sudden shutdown at 20–30% on the BLP875 after installation
This is a voltage cliff issue, not a capacity fault. Under peak modem or screen load, the cell voltage sags below the BMS cutoff threshold before the fuel gauge reports zero. It happens most often on a new cell before the first full calibration cycle. Run one full discharge to auto-shutdown and recharge completely without interruption. After that cycle the gauge IC maps the actual cutoff voltage against the reported percentage and the premature shutdowns stop.