BLP857 Oppo Realme GT Neo Replacement Battery 3.87V 4300mAh

Oppo Realme GT Neo Series — 3.87V Li-Polymer Replacement Battery (BLP857)

This is a 3.87V, 4300mAh (16.64Wh) Li-Polymer replacement battery for the Realme GT Neo, Realme GT Neo Flash 5G 2021, Realme GT Neo 5G 2021, and RMX3350. It carries the OEM part number BLP857 and fits directly into the original battery bay. Use this when the stock cell no longer holds charge or the phone shuts down unexpectedly under load.

• GT Neo and RMX3350 platform fitment: These models share the same physical envelope, connector pinout, and BMS handshake protocol. The BLP857 cell is specified across all four variants because the charge IC and fuel gauge IC reference the same voltage profile — one cell covers the full range without adaptation.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a GT Neo unit, confirming BMS communication, charge termination at rated voltage, and correct protection trip on over-discharge. The cell accepted both standard and VOOC fast charge without rejection on the second cycle.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity defect. Under modem load or peak display brightness, the cell voltage drops faster than the fuel gauge IC predicts, crossing the low-voltage cutoff threshold while the reported percentage still reads high. The fuel gauge IC was calibrated to the old, degraded cell's discharge curve and cannot immediately map the new cell's steeper voltage response. Run one full discharge to automatic shutdown, then charge uninterrupted to 100% — this resets the coulomb counter baseline and the symptom clears.

VOOC fast charge not initiating after battery swap

On the first cycle after a cell replacement, the charge IC re-handshakes with the BMS on the new cell. If VOOC or SUPERVOOC negotiation fails to complete, the phone falls back to standard 5W input. This is not a fault with the adapter or cable — it is the charge IC completing its initialisation against a new BMS. Charge once at standard speed to full capacity, then reconnect with the VOOC adapter. Fast charge resumes once the charge IC has logged a complete cycle on the new cell.