About this replacement
Vivo V40 Lite / Y100i 5G — 3.91V Li-Polymer Replacement Battery (BA27)
The BA27 is the OEM-referenced lithium-polymer cell for the Vivo V2279A, V40 Lite, and Y100i 5G 2023 Standard Edition. It runs at 3.91V nominal and carries a 4900mAh (19.16Wh) capacity. This replacement targets phones where the original cell no longer holds charge through a full day of use.
- V2279A / V40 Lite / Y100i 5G platform fit: These three models share the same battery bay dimensions, flex connector pinout, and power management IC voltage thresholds — all matched to the BA27's 3.91V nominal rail. Swapping between these variants does not require a different cell.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a V40 Lite chassis. The BMS accepted charge handshake on the first connection, held cutoff at 4.35V on full charge, and tripped the low-voltage floor at approximately 3.4V under load without false shutdown above that threshold.
- Fuel gauge recalibration on first use: On first installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before the coulomb counter locks in its reference — skip this and the percentage readout will be off for weeks.
Why the V40 Lite reports wrong battery percentage after a cell swap
The fuel gauge IC in these Vivo phones stores a learned discharge curve from the original cell. When a new BA27 goes in, the IC is still referencing that old curve. The result is percentage jumps, early charge completion warnings, or a readout that sits at 100% longer than it should. One full slow-charge cycle — charge to 4.35V cutoff, discharge to auto-shutdown, recharge fully — resets the coulomb counter against the actual new cell chemistry. After that cycle, percentage tracking stabilises.
Sudden shutdown at 20–30% on the replacement cell
This is a voltage cliff issue, not a capacity problem. Under high-current loads — 5G modem handshakes, screen at full brightness, GPS active simultaneously — the cell voltage drops faster than the fuel gauge IC can track. When terminal voltage dips below the protection threshold, the BMS cuts power even though the reported percentage still looks healthy. The fix is to run the calibration cycle described above so the IC learns the real voltage-to-capacity relationship of the new cell. If shutdowns continue after two full cycles, check that the flex connector is fully seated — a partial connection raises internal resistance and worsens voltage sag under load.