About this replacement
BBK VIVO S7 / E1T / Y3t Series — 3.7V Li-ion Replacement Battery (BK-B-49)
This is a 3.7V, 1200mAh Li-ion cell for the BBK VIVO S7, VIVO S7t, VIVO E1T, and VIVO Y3t smartphones. It replaces OEM parts BK-B-49 and BK-B-42. Dimensions are 63.95 × 43.41 × 4.54mm — measure your original before fitting.
- VIVO S7 and E1T platform fit: These models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. One cell covers all listed variants without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on VIVO hardware and confirmed BMS communication, thermal cutoff response, and charge termination voltage at 4.2V behaved within spec.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging is applied to an uncalibrated cell.
Sudden shutdown at 20–30% on the VIVO S7 after a cell swap
A new cell has a different internal resistance profile than the aged cell the fuel gauge IC was calibrated against. Under high-draw loads — active modem, screen at full brightness, GPS — the cell voltage drops faster than the gauge predicts. The phone's protection circuit reads a voltage cliff and cuts power before the displayed percentage reaches zero. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the coulomb counter to resync to the new cell curve and usually resolves this within two cycles.
VIVO S7 not powering on after the replacement cell sat in storage
Li-ion cells self-discharge during storage. If the cell voltage drops below 2.5V, the BMS enters lockout mode and blocks current flow to protect the cell from damage. Plugging in a charger won't start a normal charge cycle — the BMS needs a low-current trickle to recover. Connect the phone to a wall adapter rated at 5V and leave it for 15–20 minutes without pressing the power button; the charge IC will apply a recovery current that brings the cell above the BMS re-enable threshold, typically around 2.9V.