B-G5 BBK VIVO X27 Compatible Battery 3.85V 3900mAh

BBK Vivo X27 / X27A (V1829A, V1829) — 3.85V Li-Polymer Replacement Battery (B-G5)

The B-G5 is the OEM-matched Li-Polymer cell for the Vivo X27, X27A, V1829A, and V1829 smartphones. It runs at 3.85V with a 3900mAh (15.02Wh) capacity. If your X27 no longer holds a charge, shuts down unexpectedly, or won't power on, this cell replaces the degraded unit directly.

• V1829 / V1829A platform fit: The X27 and X27A share the V1829 board revision, which means the same BMS handshake protocol and connector pinout. Both models accept the B-G5 without modification to the flex cable or charge IC configuration.
• Bench tested on actual hardware: We cycled this cell on a V1829A unit and confirmed the BMS accepted charge on the first connection, passed overvoltage and overcurrent cutoff checks, and reported cell chemistry correctly to the OS fuel gauge IC.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-charge cycle at standard rate. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current charging pushes load into an uncalibrated cell.

Sudden shutdown at 20–30% on the Vivo X27 after a cell swap

The X27 fuel gauge IC stores a learned discharge curve from the old, degraded cell. After a swap, that stored curve no longer matches the new cell's voltage-to-capacity relationship. Under modem or display load, the phone samples cell voltage, sees it drop below the threshold predicted by the old curve, and triggers an emergency shutdown — even though real capacity remains. One full slow-discharge cycle forces the coulomb counter to relearn the new cell's profile and eliminates the false cutoff.

USB fast charging not activating after replacement on the X27

Vivo's proprietary fast charge protocol requires the charge IC to confirm cell impedance is within an acceptable range before switching into high-current mode. A freshly installed cell with a full formation charge may present a slightly different impedance signature on the first cycle, causing the charge IC to fall back to standard 5V/1A. This is not a fault in the replacement cell. Complete one full standard charge cycle first — impedance normalises, and fast charge activates automatically on the next connection without any manual step.