Vivo iQOO Neo 855 B-K0 Replacement Battery 3.85V 4350mAh

Vivo iQOO Neo 855 / V1936 — 3.85V Li-Polymer Replacement Battery (B-K0)

This is a 3.85V, 4350mAh Li-Polymer cell for the Vivo iQOO Neo 855, V1936, and V1936A smartphones. It replaces the original B-K0 battery when capacity has degraded from normal charge cycles. Dimensions are 85.50 × 64.40 × 4.70mm — a direct physical match to the factory cell bay.

• iQOO Neo 855 / V1936 platform fit: The V1936 and V1936A share the same battery bay geometry, connector pin-out, and BMS handshake protocol as the standard iQOO Neo 855 — one cell spec covers all three variants without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the iQOO Neo 855 platform and confirmed the BMS accepted the cell at full negotiated charge current without triggering a fault cutoff.
• Fuel gauge recalibration after swap: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle at standard current. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging begins on an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on the iQOO Neo 855 after a cell swap

The fuel gauge IC on the V1936 platform calculates remaining capacity against a discharge curve it learned from the original cell. A new cell has a different internal resistance profile, so the IC underestimates how much voltage drop will occur under load from the modem or display. When the processor draws a current spike, the cell voltage dips below the BMS cutoff threshold even though the reported percentage looks safe. One full discharge-charge cycle at standard current forces the coulomb counter to relearn the curve and eliminates most premature shutdowns.

USB fast charging not recognised on the first cycle after replacement

After fitting a new B-K0 cell, some users find the iQOO Neo 855 falls back to standard 5V charging rather than negotiating its higher-voltage fast charge protocol. The charge IC checks the BMS state before escalating voltage — on the first cycle, the new cell's impedance reading can cause the IC to stay conservative. Charge the phone once at standard current until full, then reconnect with the fast charger. The IC re-checks impedance on the second session and typically restores the full charge rate at that point.