BBK VIVO S1 Replacement Battery BK-B-45 3.7V 1200mAh

BBK VIVO S1 / V2 / S6 — 3.7V Li-ion Replacement Battery (BK-B-45)

This is a 3.7V, 1200mAh Li-ion cell built to the BK-B-45 specification. It fits the VIVO S1, VIVO V2, and VIVO S6 smartphones. Swap it when the original cell no longer holds a usable charge through a normal day.

• VIVO S1, V2, and S6 compatibility: All three models share the same battery bay geometry, connector pinout, and BMS handshake protocol — which is why a single BK-B-45 cell covers the full trio without modification.
• Bench tested on actual hardware: We ran this cell through charge-discharge cycles on a VIVO S1 unit and confirmed the BMS accepted the cell, reported state-of-charge correctly after one full cycle, and did not trigger a high-temperature cutoff during a standard 5V/1A charge.
• Fuel gauge recalibration on first use: Disable fast charging for the first complete discharge-charge cycle after installation. The fuel gauge IC shipped in these phones calibrates its coulomb counter against the cell's actual discharge curve — pushing high current into an uncalibrated cell skews percentage readings for weeks.

Sudden shutdown at 20–30% on a fresh BK-B-45 cell

A new cell has a steeper voltage drop-off curve near the bottom of its charge range than a worn cell does. The VIVO's fuel gauge IC is still calibrated to the old cell's curve, so it reads 25% when the real terminal voltage is already near the BMS low-voltage cutoff. Under the load spike from the modem or display, voltage dips below the cutoff threshold and the phone shuts down. One full discharge-charge cycle — without fast charging — resets the coulomb counter and moves the shutdown point back down where it belongs.

Phone will not power on after the replacement cell sat in storage

Li-ion cells self-discharge during storage, and a BK-B-45 cell stored for several months can drop below 2.5V per cell — the point at which the BMS locks out all charge current as a safety measure. The phone shows nothing when plugged in because the BMS is blocking current before it can reach the charging IC. Connect the phone to a 5V/1A charger — not a fast charger — and leave it undisturbed for 20–30 minutes. Most BMS circuits include a trickle-recovery path that accepts a small pre-charge current at this voltage, which lifts the cell above the lockout threshold and allows normal charging to resume.