Oppo A3s BLP673 Replacement Battery 3.85V 4200mAh

Oppo A3s / CPH1805 — 3.85V Li-Polymer Replacement Battery (BLP673)

The BLP673 is a 3.85V, 4200mAh Li-Polymer cell that fits the Oppo A3s, A3s Dual SIM, A3s Dual SIM TD-LTE, and CPH1805 variants. It replaces the original cell when capacity has dropped to the point where the phone can no longer hold a usable charge through a normal day. Dimensions are 87.62 × 63.86 × 4.08mm — measure your bay before installing if you are unsure which board revision you have.

• A3s variant coverage: The standard A3s, Dual SIM, and TD-LTE builds all share the same battery bay geometry and BMS handshake protocol. The BLP673 connector and cell footprint are identical across these variants, so one part covers the full CPH1805 family without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on an A3s board. The BMS accepted the charge IC handshake cleanly, held voltage above 3.6V through mid-discharge, and tripped cutoff at the correct low-voltage threshold without false termination.
• First-cycle fast charge caution: After installation, disable VOOC or any fast-charge mode for the first complete discharge-charge cycle. The fuel gauge IC is still calibrated to the old cell's discharge curve. Running a slow cycle first lets it remap against the new cell before high-current charging pushes into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on the Oppo A3s after a cell swap

This is a voltage cliff issue, not a capacity fault. Under heavy modem load or peak screen brightness, a new cell with an uncalibrated fuel gauge IC can sag below the system's minimum voltage threshold before the reported percentage reaches zero. The A3s processor cuts power immediately to protect itself — the percentage on screen was simply wrong. Run one full discharge to 0% and a full charge to 100% without interruption, and the fuel gauge will re-anchor its curve to the new cell's actual voltage profile.

Phone won't power on after the replacement battery sat in storage

Li-Polymer cells in storage self-discharge slowly. If the BLP673 dropped below approximately 2.5V per cell before installation, the BMS enters lockout and will not pass current to the board. Plug the phone into a wall charger — not a PC USB port — and leave it for 15–20 minutes without pressing the power button. The charge IC trickle-charges the cell back above the BMS recovery threshold, typically around 2.8–3.0V, at which point the BMS releases and normal charging resumes.