Vivo Y100i 5G BA08 Replacement Battery 3.91V 4900mAh

Vivo Y100i 5G 2023 Standard Edition — 3.91V Li-Polymer Replacement Battery (BA08)

This is a 3.91V, 4900mAh (19.16Wh) Li-Polymer replacement battery for the Vivo Y100i 5G 2023 Standard Edition (V2279A). It replaces OEM part BA08 when the original cell has degraded and no longer holds adequate charge. The replacement restores full power delivery to the processor, display, and 5G modem.

• Y100i 5G and V2279A compatibility: Both model designations share the same PCB layout, connector pinout, and BMS handshake protocol — the BA08 cell fits both without any hardware modification.
• Bench tested on actual hardware: We cycled this cell on a V2279A unit and confirmed the BMS accepted the new cell, voltage reported correctly at 3.91V nominal, and the charge IC reached full termination without fault codes.
• Fuel gauge recalibration on first install: After fitting this cell, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the Vivo Y100i 5G after a cell swap

This happens when the fuel gauge IC is still calibrated to the old cell's discharge curve. The phone's voltage model expects the old cell to sustain load at 20–30% state-of-charge, but the new cell has a slightly different voltage cliff. Under 5G modem or display load, the cell voltage drops below the system's minimum threshold before the percentage reaches zero. One full discharge-charge cycle at standard (non-fast) charging corrects the coulomb counter and eliminates the false cutoff.

USB fast charging not activating after BA08 replacement

On the first cycle after installation, the charge IC may not negotiate the proprietary fast-charge protocol because the BMS has not yet confirmed cell state to the handshake controller. This is normal. Charge the device once to 100% using the standard OEM cable and charger without triggering fast charge. On the second cycle, fast charging typically activates once the BMS has logged a full charge termination event and accepted the cell as valid.