Oppo A1K BLP711 Replacement Battery 3.85V 4000mAh

Oppo A1K / CPH1923 — 3.85V Li-Polymer Replacement Battery (BLP711)

This is a 3.85V, 4000mAh Li-Polymer replacement battery for the Oppo A1K smartphone (CPH1923). It replaces the original BLP711 cell and restores power to the display, processor, and wireless radios. Dimensions are 87.35 × 60.20 × 4.00mm — confirm your existing cell before ordering.

• A1K / CPH1923 platform fit: The A1K and CPH1923 are the same hardware variant sold across different regions. Both use the BLP711 cell on a shared voltage rail with the same connector orientation and BMS handshake — no adapter or modification needed.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the A1K board. The BMS accepted charge handoff without error flags, and protection circuits tripped correctly at the expected low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: After fitting this cell, disable VOOC fast charging for the first complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve accurately before high-current charging pushes current into an uncalibrated coulomb counter.

Why the Oppo A1K shuts down suddenly at 20–30% after a battery swap

The A1K's fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, the old curve no longer matches the actual voltage profile of the replacement. Under modem or screen load, the phone reads 25% but the cell voltage has already dropped below the safe floor — the BMS cuts power before the OS can log a low-battery event. One full discharge-to-shutdown followed by a full charge resets the coulomb counter and resolves the mismatch. After that cycle, percentage readings stabilise.

VOOC fast charge not activating on the first cycle after fitting

Oppo's VOOC protocol negotiates with the battery's BMS before switching to high-current charge mode. On the first cycle with a new cell, the charge IC runs a standard 5V/1A handshake while it verifies BMS parameters — VOOC will not engage until this check passes. The phone may show a slow-charge icon even with a VOOC adapter plugged in. Let the first full charge complete at standard rate; VOOC activates normally from the second cycle onward once the charge IC has logged a valid BMS response.