Vivo X9s Plus B-C2 Compatible Battery 3.85V 3950mAh

Vivo X9s Plus — 3.85V Li-Polymer Replacement Battery (B-C2)

This 3.85V, 3950mAh lithium-polymer cell replaces the original B-C2 battery in the Vivo X9s Plus smartphone. It fits the X9s Plus directly, matching the OEM voltage rail, connector, and physical dimensions (85.05 × 67.60 × 4.10mm). Swap it in when the original cell can no longer hold a charge through a normal day of use.

• X9s Plus platform fit: The X9s Plus uses a dedicated battery bay sized for this exact cell footprint. The B-C2 part number ties this cell to the Vivo X-series BMS handshake — the charge IC on this phone negotiates current limits with the cell's internal protection circuit, so voltage and connector alignment both matter.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge passes on the X9s Plus. The BMS accepted the cell without triggering an over-voltage or under-voltage cutoff, and the charge IC stepped through trickle, constant-current, and constant-voltage phases cleanly.
• Fuel gauge recalibration after install: On first use, disable fast charging and run one full discharge down to automatic shutdown, then charge to 100% on a standard 5V charge. This lets the coulomb counter in the fuel gauge IC map its reference curve against the new cell before high-current charging begins.

Why the X9s Plus reports wrong battery percentage after a cell swap

The X9s Plus uses a fuel gauge IC that tracks charge state using a learned discharge curve from the original cell. When you install a fresh 3950mAh cell, that stored curve no longer matches the new cell's actual voltage-vs-capacity profile. The IC may show 80% when the cell is at 60%, or drop suddenly from 30% to zero. One full discharge-charge cycle without interruption forces the coulomb counter to relearn the curve against the new cell. After that cycle, percentage readouts stabilise.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the BMS cutoff threshold under a high-current load — typically the modem, GPS, or display all drawing at once — even though the fuel gauge still shows charge remaining. A freshly installed cell that has not been through a calibration cycle will have a mismatched reference point, making this cliff worse. Run one uninterrupted discharge to shutdown and a full charge back to 100%. If shutdowns continue past the second cycle, check that the cell connector is fully seated — a partial contact raises internal resistance and causes the same voltage sag under load.