About this replacement
Vivo S1 Pro / V1945 — 3.85V Li-Polymer Replacement Battery (B-G6)
This is a 4000mAh Li-Polymer replacement battery for the Vivo S1 Pro and V1945 smartphones. It runs at 3.85V nominal and carries OEM part number B-G6. Swap it in when your original cell can no longer hold charge through a full day of use.
- S1 Pro and V1945 compatibility: Both devices share the same board layout, connector pinout, and BMS handshake protocol — the B-G6 cell covers both without any modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the S1 Pro platform. The BMS accepted the cell without fault codes, and the fuel gauge IC began tracking state-of-charge after the first complete cycle.
- First-cycle calibration tip: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.
Why the S1 Pro reports wrong battery percentage after a cell swap
The S1 Pro uses a coulomb counter that stores learned discharge data from the old cell. When a new cell goes in, that stored curve no longer matches the actual cell chemistry. The fuel gauge IC reads state-of-charge against stale data, so the percentage shown on screen drifts from real capacity. One full discharge — drain to automatic power-off, then charge uninterrupted to 100% — forces the IC to rewrite its reference curve against the new cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem or display draws a short high-current burst and the cell voltage drops below the BMS cutoff threshold — even though the displayed percentage looks safe. A fresh cell with an uncalibrated fuel gauge IC is especially vulnerable in the first few cycles. Run the full calibration cycle described above. After two complete cycles, the IC learns the actual voltage-to-capacity curve and the shutdowns stop. If they persist after three cycles, check that resting cell voltage reads at least 3.7V with a meter before reinstalling.