BLP729 Oppo Realme 5i Replacement Battery 3.85V 4900mAh

Oppo Realme 5i / Realme C3 — 3.85V Li-Polymer Replacement Battery (BLP729)

The BLP729 is a 3.85V, 4900mAh Li-Polymer cell that fits the Realme 5i, Realme 5, Realme C3, and Realme C11. It replaces the original factory cell when capacity has dropped, the phone shuts off unexpectedly, or charge cycles no longer hold. Capacity is 18.87Wh.

• Realme 5 series and C-series fit: These models share the BLP729 connector, cell footprint, and BMS handshake profile — same voltage rail at 3.85V nominal and matching flex tab position means one cell covers the full compatibility group without adapters.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Realme 5i unit. The BMS accepted the cell, passed the protection circuit check, and the charge IC reached full termination voltage without fault flags.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before the coulomb counter locks in its reference points.

Sudden shutdown at 20–30% on the Realme 5i after a cell swap

This happens because the fuel gauge IC is still running the discharge curve it learned from the old, degraded cell. The new cell hits a steeper voltage drop under screen or modem load than the IC expects, so it triggers a low-voltage shutdown before the percentage reaches zero. It is not a faulty cell — it is a calibration mismatch. Run one full discharge from 100% to auto-off, then charge uninterrupted to 100% without pulling the cable early, and the IC will re-anchor its curve to the new cell.

Phone reports wrong percentage after BLP729 replacement

The Realme 5i uses a coulomb counter that tracks charge in and out relative to a stored full-capacity value from the previous cell. After swapping to a new 4900mAh cell, that stored value is stale and the reported percentage drifts — often reading 15–20% high before the first real drop. The fix is one uninterrupted full cycle: discharge until the phone powers off on its own, then charge straight to 100% at standard rate with fast charge off. After that cycle, the fuel gauge IC writes a new full-capacity reference and percentage accuracy returns to within a few points.