BBK VIVO E1 Replacement Battery BK-B-40 3.7V 1200mAh

BBK VIVO E1 / V305 / i710 — 3.7V Li-ion Replacement Battery (BK-B-40)

This is a 3.7V, 1200mAh Li-ion cell built to the BK-B-40 specification. It fits the VIVO E1, VIVO i710, and VIVO V305 smartphones. Swap it in when the original cell no longer holds a charge or the phone shuts down unexpectedly under load.

• VIVO E1, i710, and V305 compatibility: All three models run the same 3.7V single-cell architecture with identical connector pinout and BMS handshake protocol. One cell covers the full range without any wiring or fitment differences.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on VIVO E1 hardware. The BMS accepted the charge controller handshake without fault, and the protection circuit tripped correctly at the low-voltage cutoff threshold — no runaway or thermal event observed.
• Fuel gauge recalibration on first install: On first use after installation, disable fast charging and run one full discharge-charge cycle at standard current. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before the charge IC pushes higher current into an uncalibrated state.

Sudden shutdown at 20–30% on the VIVO E1 after a cell swap

The VIVO E1's fuel gauge IC stores a discharge curve calibrated to the original cell. A new cell with a slightly different internal resistance profile will show a voltage cliff at a different state-of-charge point than the IC expects. When screen brightness or the modem draws a spike, the cell voltage drops below the shutdown threshold before the reported percentage reaches zero. The fix is one complete unconstrained discharge to auto-off followed by a full charge — this forces the coulomb counter to resync to the new cell's actual curve. After that cycle, the reported percentage tracks accurately against real remaining capacity.

Phone won't power on after the replacement cell sat in storage

Li-ion cells self-discharge during storage. If the cell voltage has dropped below approximately 2.5V, the BMS enters lockout mode and blocks current flow to protect the cell from damage. The phone will show no response — no boot screen, no charging indicator on plug-in. Connect the phone to a wall adapter and leave it for 15–20 minutes without pressing any button; the charge IC will trickle current into the cell until voltage climbs above the BMS re-enable threshold, typically around 2.9–3.0V. Once the charging indicator appears, the BMS has re-initialised and normal charging resumes.