Vivo iQOO 3 B-K7 Replacement Battery 3.85V 4400mAh

Vivo iQOO 3 Series — 3.85V Li-Polymer Replacement Battery (B-K7)

The B-K7 is a 3.85V, 4400mAh Li-Polymer cell for the Vivo iQOO 3, iQOO 3 5G, V1955, and V1955A. It replaces degraded original cells that no longer hold adequate charge. At 16.94Wh, capacity matches the factory specification for these models.

• iQOO 3 and V1955 platform fit: The iQOO 3, iQOO 3 5G, V1955, and V1955A share the same battery bay dimensions, connector pinout, and BMS handshake protocol — all four accept the B-K7 cell without modification.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the iQOO 3 platform. The BMS communicated correctly with the fuel gauge IC, and charge termination triggered at the expected voltage ceiling on both standard and fast-charge profiles.
• First-cycle fuel gauge reset: After installation, disable fast charging and run one complete discharge-charge cycle at standard rate. The fuel gauge IC is calibrated to the old cell's discharge curve — one full cycle at low current lets it recalibrate against the new cell before high-current fast charging begins.

Why the iQOO 3 reports wrong battery percentage after a cell swap

The iQOO 3 uses a coulomb counter integrated into the fuel gauge IC, which builds its charge model from the previous cell's discharge history. After swapping to a new B-K7 cell, that stored model no longer matches actual cell chemistry, so the reported percentage drifts from reality. The fix is one full discharge to below 5% followed by a slow, uninterrupted charge to 100% — this forces the IC to rewrite its reference curve against the new cell. Until that cycle completes, percentage readouts may appear to jump or stall at unexpected points.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC's voltage-to-capacity map is still matched to the worn original cell, which had a flatter discharge curve at low state-of-charge. The new B-K7 cell has a steeper voltage cliff below roughly 3.5V per cell, so under modem or display load the terminal voltage drops faster than the IC predicts. The phone interprets the sudden voltage drop as a critical low event and shuts down even though the percentage display still shows charge remaining. Run one full calibration cycle — discharge to near-zero, then charge uninterrupted to 100% at standard rate — and the shutdowns will stop.