Vivo Y01 Replacement Battery B-S7 3.87V 4850mAh

Vivo Y01 — 3.87V Li-Polymer Replacement Battery (B-S7)

This 3.87V, 4850mAh Li-Polymer cell replaces the OEM B-S7 battery in the Vivo Y01 smartphone. It fits the Y01 directly, matching the original connector, BMS communication lines, and physical footprint. Dimensions are 96.00 × 64.80 × 4.40mm — verify against your existing cell before fitting.

• Vivo Y01 fit: The Y01 uses the B-S7 cell across its production run. The BMS on this phone handshakes over the same three-wire connector as the OEM unit, so the fuel gauge IC picks up the new cell without requiring any hardware modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Y01 platform. The BMS accepted the cell on first connection, and the charge IC ramped to full current without flagging a fault. Fuel gauge readings stabilised after one complete cycle.
• First-cycle fast charge tip: On first use after installation, disable fast charging and run one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes amperage into an uncalibrated cell.

Why the Y01 reports wrong battery percentage after a cell swap

The Vivo Y01 uses a coulomb counter that was calibrated to the original cell's discharge curve. When a new cell goes in, the counter still references old capacity data, so the percentage shown on screen drifts from actual charge state. The fix is straightforward: run the phone down to auto-shutdown, then charge uninterrupted to 100% without pulling the cable early. After that single full cycle, the fuel gauge IC rewrites its reference curve against the new cell and percentage accuracy returns to normal.

Sudden shutdown at 20–30% remaining on the replacement cell

This happens when the fuel gauge IC has not yet recalibrated and the cell voltage drops below the modem or display load threshold before the percentage reaches zero. The phone's processor sees a voltage cliff — the cell can no longer sustain load current at that state of charge — and the BMS cuts output to protect the cell. It is not a faulty battery; it is an uncalibrated gauge reading a new discharge curve as if it were the old one. Complete one full discharge-charge cycle and check that voltage at shutdown is at or above 3.40V per cell to confirm normal BMS cutoff behaviour.