Oppo Reno4 SE Replacement Battery BLP811 7.74V 1700mAh

Oppo Reno4 SE / Reno5 / Reno5k — 7.74V Li-Polymer Replacement Battery (BLP811)

This is a 7.74V, 1700mAh Li-Polymer replacement battery for the Oppo Reno4 SE, Reno5, and Reno5k smartphones. It uses OEM part number BLP811 and fits the internal battery bay directly. Total energy is 13.16Wh.

• Reno4 SE, Reno5, and Reno5k compatibility: All three models share the BLP811 cell format, the same connector pinout, and a compatible BMS handshake with the charge IC on the motherboard. Swapping between these variants does not require firmware changes.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Reno5 platform. The BMS accepted charge handshake without fault codes, and the fuel gauge IC tracked state-of-charge through two full cycles before stabilising.
• First-cycle fast charge protocol: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated cell.

Why the Reno4 SE reports wrong battery percentage after a cell swap

The fuel gauge IC on these Oppo devices stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual chemistry. The IC keeps reporting percentage against the old data until it recalibrates. Run one full discharge down to automatic shutdown, then charge uninterrupted to 100% — the coulomb counter resets against the new cell after that cycle.

Sudden shutdown at 20–30% on the BLP811 replacement cell

This happens when the cell voltage drops sharply under load — screen brightness, modem activity, or GPS all pull current spikes that a partially calibrated cell cannot sustain. The BMS cuts power at roughly 3.2V per cell to protect the chemistry, even though the OS still shows charge remaining. It is not a defective battery — it is the fuel gauge IC reading a stale state-of-charge estimate. One full discharge-charge cycle re-anchors the percentage to the actual voltage curve, and the shutdowns stop.