BBK VIVO Z5x Replacement Battery B-G7 3.85V 4900mAh

BBK VIVO Z5x Series — 3.85V Li-Polymer Replacement Battery (B-G7)

This is a 3.85V, 4900mAh (18.87Wh) Li-Polymer cell carrying OEM part number B-G7. It fits the VIVO Z5x, VIVO Z5x Premium Edition, VIVO Z5x Premium Edition Dual SIM, and VIVO Z5x Premium Edition Dual SIM TD-LTE, along with nine additional regional variants of the same platform. If the original cell is swelling, dropping charge rapidly, or refusing to hold voltage under load, this is the direct swap.

• Z5x platform compatibility: All listed variants share the same physical footprint (90.10 × 65.10 × 4.70mm), the same 3.85V nominal rail, and the same B-G7 connector pinout. The BMS handshake across dual-SIM and TD-LTE variants uses the same authentication line, so no firmware-level rejection occurs on recognised hardware.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Z5x unit. The BMS accepted the cell without triggering a fault state, charge IC transitioned correctly from CC to CV phase, and the protection circuit cut off cleanly at the low-voltage threshold.
• First-cycle fast charge protocol: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's actual discharge curve before high-current charging pushes current into an uncalibrated cell — preventing premature charge termination and skewed percentage readings from the first day.

Why the VIVO Z5x reports wrong battery percentage after a cell swap

The Z5x fuel gauge IC stores a learned discharge curve from the original cell in non-volatile memory. When a new cell goes in, the IC continues referencing that old curve. The mismatch causes the percentage readout to drift — often reading 30% while the actual cell voltage is already near 3.5V. One full uninterrupted discharge down to automatic shutdown, followed by a complete charge to 100%, forces the IC to rewrite its reference curve against the new cell's actual characteristics. After that single cycle, percentage accuracy stabilises.

Sudden shutdown at 15–25% on the Z5x after replacement

This is a voltage cliff, not a capacity fault. Under peak load — simultaneous modem activity, screen-on, and background sync — the cell voltage sags faster than the fuel gauge predicts, crossing the hardware protection threshold while the display still shows charge remaining. It is most common in the first two cycles before the coulomb counter recalibrates. Run two full discharge-charge cycles without fast charging enabled. If shutdown persists past cycle three at the same percentage, check that the connector is fully seated; a partially engaged tab increases contact resistance and worsens sag, typically dropping an extra 0.1–0.2V under load.