About this replacement
Oppo Realme 1 / F7 Youth — 3.85V Li-Polymer Replacement Battery (BLP665)
This is a 3350mAh, 3.85V lithium-polymer cell carrying OEM part number BLP665. It fits the Realme 1 (CPH1861, CPH1859) and the F7 Youth — all variants that share the same battery bay dimensions and connector. Use the product data capacity figure: 3350mAh / 12.9Wh.
- CPH1861, CPH1859, and F7 Youth compatibility: These models run the same 3.85V power rail, use an identical flex connector, and share the same BMS handshake protocol — which is why one cell covers all three. Swapping between these variants requires no wiring modification.
- Bench tested on actual hardware: We cycled this cell on a CPH1861 unit and monitored BMS charge-termination voltage. The protection circuit cut charge at 4.35V and triggered low-voltage cutoff at 3.0V — both within spec for this platform.
- Fuel gauge recalibration after swap: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes into an uncalibrated coulomb counter.
Sudden shutdown at 20–30% on the BLP665 replacement cell
This is a voltage cliff issue, not a capacity defect. When the modem fires a transmission burst or the screen jumps to full brightness, instantaneous current draw spikes. If the fuel gauge IC is still calibrated to the old cell's discharge curve, it misreads state-of-charge at high-load moments. The cell voltage sags below the BMS cutoff threshold even though the reported percentage looks safe. One full discharge-charge cycle with fast charging off resets the coulomb counter and eliminates most of these shutdowns.
Phone reports wrong battery percentage after cell swap
The Realme 1's fuel gauge IC stores an internal model of the old cell's impedance and voltage-to-capacity curve. After fitting a new BLP665, those stored values no longer match the fresh cell's characteristics, so the percentage reading drifts — often showing 100% prematurely or dropping suddenly. Drain the battery to automatic shutdown, then charge uninterrupted to 100% with fast charging disabled. After that single cycle the coulomb counter resets to the new cell's actual curve and percentage accuracy stabilises.