Oppo Reno6 4G BLP819 Compatible Battery 3.87V 4200mAh

Oppo Reno6 4G / Reno 5Z 5G — 3.87V Li-Polymer Replacement Battery (BLP819)

The BLP819 is a 3.87V, 4200mAh (16.25Wh) Li-Polymer cell that fits the Oppo Reno6 4G (CPH2235) and Reno 5Z 5G 2021 (CPH2211). It replaces the internal battery when the original cell can no longer hold a usable charge or causes unexpected shutdowns. Capacity figure is taken directly from the product specification — no rounding, no inflation.

• CPH2235 and CPH2211 platform fit: Both models share the BLP819 footprint — same 86.40 × 62.90 × 5.00 mm envelope, same flex connector pinout, and compatible BMS handshake with the PMIC on each board. The cell slots without modification.
• Bench tested on actual hardware: We cycled this cell on a CPH2235 unit and monitored BMS communication through full charge and discharge. The protection circuit triggered correctly at the low-voltage cutoff and the charge IC accepted both standard and VOOC charge sessions without fault codes.
• Fuel gauge recalibration after installation: On first use after fitting, disable fast charging and run one complete discharge-charge cycle at standard rate. This gives the fuel gauge IC a clean discharge curve to map against the new cell before VOOC pushes high current into an uncalibrated coulomb counter.

Why the Reno6 4G reports wrong battery percentage after a cell swap

The fuel gauge IC on the CPH2235 board stores a learned discharge curve from the original cell. When you install a new BLP819, that stored curve no longer matches the new cell's actual voltage profile. The IC interpolates percentage from voltage points calibrated to the old, degraded cell — so it reads too high or too low until it relearns. One full slow-charge cycle, starting from below 10%, forces the coulomb counter to reset its endpoint references against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the display or modem draws a high current burst and the cell voltage sags below the BMS cutoff threshold — even though the gauge still reads 20% or higher. It is a calibration gap, not a faulty cell. The fuel gauge IC assigned that percentage to a voltage point the old cell could sustain, but the new cell's internal resistance profile is different. Run the recalibration cycle described above; after one full slow discharge to shutdown and a complete recharge, the gauge maps the correct voltage-to-percentage relationship and the early cutoff stops.