About this replacement
Oppo Realme X7 Pro 5G — 7.74V Li-Polymer Replacement Battery (BLP799)
This is a 7.74V, 2200mAh Li-Polymer replacement battery for the Realme X7 Pro 5G (RMX2121 / R2121) and X30 Pro 5G. It fits directly where the original BLP799 cell sits. Use the Capacity figure here — 2200mAh — not third-party listings that quote different numbers.
- RMX2121 and X30 Pro 5G compatibility: Both devices run the same dual-cell Li-Polymer pack on a shared BMS connector pinout with identical voltage rails. One cell swap covers the full compatibility list without any hardware modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the RMX2121 board. The BMS accepted the cell without fault flags, and the charge IC handed off to trickle at the expected cutoff voltage.
- Fuel gauge recalibration on first use: After installation, disable fast charging and run one full discharge-to-charge cycle at standard rate. The fuel gauge IC maps the new cell's discharge curve during that first cycle — without it, the coulomb counter reports against the old cell profile.
USB-PD fast charge not working on first cycle after replacement
The Realme X7 Pro 5G uses a proprietary VOOC/SuperDart charge protocol layered on top of the USB-PD handshake. When a new BLP799 cell is installed, the charge IC runs an initial impedance check before it will accept high-current negotiation. On the first cycle, the device often falls back to standard 5V charging because this check has not completed. Complete one full standard charge cycle first. After that, SuperDart handshake resumes normally on subsequent plugs.
Sudden shutdown at 20–30% after cell replacement
This is a voltage-cliff failure — not a capacity problem. Under heavy modem or display load, the new cell momentarily drops below the BMS shutdown threshold even though the fuel gauge still reads 20–30%. It happens because the coulomb counter is still calibrated to the old cell's internal resistance curve. Run two full unconstrained discharge cycles without fast charging. After that, the fuel gauge IC maps the actual voltage-to-capacity curve of the new cell, and the premature shutdowns stop. If they persist past three cycles, check that the cell connector is fully seated and reads above 3.87V per cell at rest.