BK-B-76 BBK VIVO Y27 Compatible Battery 3.8V 2250mAh

BBK VIVO Y27 — 3.8V Li-Polymer Replacement Battery (BK-B-76)

This is a 3.8V, 2250mAh (8.55Wh) Li-Polymer cell built to the BK-B-76 specification for the VIVO Y27 smartphone. It replaces a degraded or failed original battery when the phone can no longer hold a charge through a normal day. The cell matches the original's dimensions (79.10 × 63.50 × 3.50 mm) and connector pinout.

• VIVO Y27 fitment: The Y27 uses a single-cell Li-Polymer pack with a proprietary flat connector tied to the phone's charge IC and fuel gauge. This cell matches that connector and the BMS communication expected by the VIVO Y27 motherboard — no adapter or modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a VIVO Y27 board. The BMS accepted the cell without fault codes, and the charge IC ramped current normally through CC and CV phases. No thermal events were recorded.
• First-cycle fuel gauge reset: On first use after installation, disable fast charging and run one full discharge-to-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before the coulomb counter locks in its calibration reference.

Why the VIVO Y27 reports wrong battery percentage after a cell swap

The Y27's fuel gauge IC stores a learned discharge curve from the original cell. After a replacement, the IC is still referencing that old curve, so the percentage shown on screen does not match the new cell's actual state of charge. This mismatch causes the reported number to jump or stall at certain levels — particularly between 80% and 100%, where the original cell's curve was steepest. One full discharge below 5% followed by a complete charge cycle forces the coulomb counter to reset its baseline. After that cycle, percentage reporting stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC has not yet recalibrated and the new cell hits a voltage cliff under modem or display load. The Y27's processor draws a sharp current spike during network handshakes, pulling cell voltage below the BMS cutoff threshold even though the displayed percentage still reads mid-range. The phone interprets the voltage drop as a fault and shuts down to protect the cell. Run two full discharge-charge cycles without fast charging — by the second cycle the fuel gauge reference aligns with the actual cell voltage, and the cutoff trigger shifts to a more accurate state-of-charge point near 3.2V.