Vivo BA18 V2344A Replacement Battery 3.91V 4850mAh

Vivo S18 Pro / V2344A — 3.91V Li-Polymer Replacement Battery (BA18)

This is a 3.91V, 4850mAh (18.96Wh) Li-Polymer cell that fits the Vivo V2344A, S18 Pro, and S18 smartphones. It replaces OEM part number BA18 using the same voltage rail and connector footprint as the factory cell. Swap it in when your original cell can no longer hold charge across a normal day of use.

• V2344A, S18, and S18 Pro compatibility: These three models share the BA18 form factor — same 90.00 × 62.20 × 4.80mm envelope, same 3.91V nominal rail, and the same BMS handshake protocol. One cell covers all three variants without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the S18 platform. The BMS accepted the charge profile correctly, protection thresholds tripped at the expected low-voltage cutoff, and the fuel gauge IC picked up the new cell without throwing fault codes.
• Fuel gauge recalibration after installation: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This lets the fuel gauge IC build an accurate discharge curve against the new cell before high-current charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the BA18 replacement cell

This is a voltage cliff problem, not a capacity problem. Under peak modem load or screen brightness, the new cell's internal resistance causes voltage to sag below the protection threshold before the percentage readout catches up. The BMS trips and the phone shuts down even though the fuel gauge still shows charge remaining. One full discharge-to-charge cycle recalibrates the coulomb counter and reduces the gap between reported and actual cell voltage. After recalibration, target a resting voltage of around 3.85–3.90V at 50% SoC as a reference point.

USB-PD fast charge not accepted on first cycle after replacement

On the first charge after a cell swap, the charge IC may fall back to standard 5V charging rather than negotiating the fast charge protocol. This happens because the BMS treats the new cell as uncharacterised and applies conservative current limits until it completes one reference cycle. Do not interpret this as a fault with the replacement cell or the charger. Run one full charge at standard rate, let the phone reach 100%, then reconnect your fast charger — the protocol negotiation should succeed on the second cycle.