About this replacement
Vivo Y77 / V2169 — 7.78V Li-Polymer Replacement Battery (B-V8)
This is a 7.78V, 2100mAh Li-Polymer replacement battery for the Vivo Y77 and V2169 smartphones. It fits directly into either model and restores full charge capacity to phones where the original cell has degraded. Voltage and capacity match the OEM specification listed under part number B-V8.
- Y77 and V2169 compatibility: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol, which is why a single cell — B-V8 — covers both. The 91.00 × 63.00 × 5.00mm form factor seats without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Y77 unit. The BMS accepted the cell without fault codes, and the charge IC progressed through pre-charge, constant-current, and constant-voltage phases without interruption.
- First-cycle fast charge protocol: On first use after installation, disable fast charging and complete one full discharge-charge cycle at standard rate. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.
Why the Vivo Y77 reports the wrong battery percentage after a cell swap
The Y77 uses a coulomb-counter fuel gauge IC that builds its charge model against the original cell's discharge curve over hundreds of cycles. When a new cell goes in, the IC still references that old curve, so displayed percentage drifts from actual cell state. The gauge needs at least one full uninterrupted discharge down to automatic shutdown, followed by a full charge to 100%, before its model resets. Until that cycle completes, readings anywhere in the 15–85% range can be off by 10–20 percentage points. Keep the phone on standard charge for that first cycle — no fast charge, no mid-cycle top-ups.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC's state-of-charge estimate is still mapped to the old cell's voltage-capacity curve. The new cell hits a voltage cliff — typically around 3.5V per cell — before the gauge reaches 0%, and the phone cuts off to protect the cell. It is not a faulty battery; it is a calibration gap. Run one complete discharge to automatic shutdown, then charge uninterrupted to 100%. After that cycle, the gauge recalibrates and shutdown should not occur above 5%.