BBK VIVO X9i B-B9 Compatible Battery 3.85V 3150mAh

BBK VIVO X9i — 3.85V Li-Polymer Replacement Battery (B-B9)

This is a 3150mAh (12.13Wh) Li-Polymer cell built to replace the original B-B9 battery in the VIVO X9i smartphone. It fits the X9i directly and matches the original voltage and physical footprint. Dimensions are 82.90 × 62.40 × 3.40mm.

• VIVO X9i fit: The X9i uses a sealed rear housing with a dedicated battery connector tied to the fuel gauge IC. This cell matches the B-B9 connector pinout and capacity spec, so the device's power management circuit accepts it without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the VIVO X9i platform. The BMS accepted charge on the first cycle, and the fuel gauge IC tracked state-of-charge without triggering a low-voltage cutoff error.
• First-cycle fuel gauge recalibration: On first use after installation, disable fast charging for one complete discharge-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 state.

Why the VIVO X9i reports wrong battery percentage after a cell swap

The X9i uses a coulomb counter to track charge state. That counter was calibrated to the old cell's internal resistance profile. A new cell has different impedance, so the stored curve no longer matches actual charge delivery. The phone may show 50% and cut off seconds later, or sit at 1% for an extended period. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to rewrite its reference curve.

Sudden shutdown at 20–30% charge on the VIVO X9i

This is a voltage cliff failure — not a capacity problem. Under modem transmission load or peak screen brightness, the cell voltage drops faster than the fuel gauge IC predicts, crossing the 3.2V hardware cutoff before the displayed percentage reaches zero. It happens most often on a fresh cell that hasn't been calibrated yet. Run one full discharge cycle with the screen on and mobile data active, then charge uninterrupted to 100% to anchor the gauge to the new cell's real voltage curve.