About this replacement
Oppo A3 / CPH1837 — 3.85V Li-Polymer Replacement Battery (BLP661)
The BLP661 is a 3.85V, 3300mAh Li-Polymer cell for the Oppo A3 and A3 Dual SIM smartphones, including the TD-LTE and CPH1837 variants. It restores power delivery to the phone's display, modem, and processor when the original cell has degraded or failed. Capacity and voltage match the OEM specification exactly.
- A3 and CPH1837 series fit: All listed A3 variants share the same BLP661 connector pinout, cell dimensions (81.52 × 64.62 × 3.65mm), and 3.85V nominal voltage rail. The charge IC and BMS handshake are consistent across the Dual SIM and TD-LTE builds, so one cell covers the full model range.
- Bench tested on actual hardware: We cycled the BLP661 through a full charge-discharge sequence on the CPH1837 board. The BMS accepted charge current at both standard and fast-charge rates, and the fuel gauge IC tracked cell voltage without error flags after the first complete cycle.
- First-cycle fuel gauge reset: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. The fuel gauge IC recalibrates its coulomb counter against the new cell's discharge curve — skipping this step leaves the IC mapping to the old cell's profile, which causes percentage errors early on.
Sudden shutdown at 20–30% on the Oppo A3 after a cell swap
The Oppo A3 shuts down abruptly at 20–30% because the fuel gauge IC is still running the degraded discharge curve from the old cell. When modem or screen load spikes, the new cell's actual terminal voltage drops below the shutdown threshold before the displayed percentage reaches zero. The IC interprets this as an immediate undervoltage event and cuts power. One full discharge cycle — draining to automatic shutdown, then charging uninterrupted to 100% — forces the coulomb counter to re-map to the new cell, and the false cutoffs stop.
Oppo A3 not powering on after the replacement battery sat in storage
Li-Polymer cells self-discharge in storage, and if the BLP661 cell dropped below approximately 2.5V, the BMS enters lockout to prevent damage from deep discharge. The phone will show no response — no logo, no charging indicator — even when plugged in. Connect the phone to a wall charger (not a USB hub) and leave it for 20–30 minutes without pressing the power button; the BMS needs a trickle current at around 3.0V before it re-enables normal charge flow. Once the screen shows the charging indicator, the cell is out of lockout and will charge normally to 3.85V.