BBK VIVO Y1 Replacement Battery BK-B-36A 3.7V 1050mAh

BBK VIVO Y1 / V303 — 3.7V Li-ion Replacement Battery (BK-B-36A)

This is a 3.7V, 1050mAh Li-ion cell built to the BK-B-36A specification. It fits the VIVO Y1 and VIVO V303 smartphones. Voltage and connector match the original, so the charge IC and fuel gauge IC can communicate with the new cell without modification.

• VIVO Y1 and V303 platform fit: Both models run the same battery bay dimensions, connector pinout, and BMS handshake. The 64.17 × 37.65 × 4.72mm cell seats flush, and the NTC thermistor line aligns correctly so the charge IC does not flag a thermal fault on first boot.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence and monitored BMS communication. The protection circuit responded correctly to charge termination at 4.2V and triggered undervoltage cutoff cleanly below 3.0V per cell.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before any high-current charging pushes current into an uncalibrated state.

Sudden shutdown at 20–30% on the VIVO Y1 after a cell swap

This is a voltage cliff issue, not a capacity problem. When the modem, screen, and CPU pull current simultaneously, a freshly installed cell that hasn't been calibrated can drop below the BMS cutoff threshold faster than the fuel gauge IC expects. The OS reads 25% remaining, but the instantaneous voltage under load dips below 3.2V and the BMS cuts power. One full discharge-charge cycle at standard charge rate — with fast charging off — resolves it by syncing the coulomb counter to the actual cell discharge curve.

Phone warm near the battery compartment on the first charge cycle

A new cell starts with slightly higher internal impedance than a broken-in one. During the first charge cycle, the charge IC on the VIVO Y1 pushes current into that higher impedance, which dissipates more heat than usual. This is normal on cycle one and typically reduces after two to three full cycles as impedance settles. If warmth continues past the third full charge, check that the battery flex connector is fully seated — a partial connection forces higher contact resistance at the pin and generates sustained heat.