Vivo S5 B-K2 Replacement Battery 3.85V 3800mAh

Vivo S5 / V1932A / V1932T — 3.85V Li-Polymer Replacement Battery (B-K2)

This is a 3.85V, 3800mAh (14.63Wh) lithium-polymer cell for the Vivo S5, S5 Dual SIM, V1932A, and V1932T smartphones. It replaces the OEM B-K2 pack when the original cell can no longer hold a usable charge across a full day. Dimensions are 73.10 × 62.60 × 5.04mm — verify your existing cell before ordering.

• S5 / V1932A / V1932T compatibility: These model numbers share the same physical footprint, connector pinout, and BMS handshake protocol. The V1932A and V1932T are regional variants of the same board revision, so one cell fits all four.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the S5 platform. The BMS communicated correctly with the charge IC, accepted the full 3800mAh capacity, and did not trigger overcurrent cutoff during screen-on load.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC build an accurate discharge curve against the new cell before high-current charging pushes into an uncalibrated state.

Sudden shutdown at 20–30% on the Vivo S5 after a cell swap

A new cell has a slightly different internal resistance curve than the worn cell the fuel gauge IC was calibrated against. Under peak load — active display, LTE modem, background sync — voltage can sag sharply even when the reported percentage looks safe. The phone's protection circuit reads this voltage drop as a low-cell event and shuts down before the displayed percentage reaches zero. One full discharge-charge cycle lets the coulomb counter remap its cutoff thresholds to the new cell's actual voltage curve, and the premature shutdowns stop.

USB fast charging not working on the first cycle after replacement

Vivo's proprietary charge protocol negotiates between the charger and the phone's charge IC on every session. With a freshly installed cell that the BMS has not yet initialised, some units refuse the high-current handshake and fall back to standard 5V charging. This is not a fault with the charger or the cell. Charge the phone once at standard rate until the battery reaches 100%, then reconnect — fast charging resumes normally once the BMS has completed its first full session.