About this replacement
Vivo Y55s / V2164A — 3.87V Li-Polymer Replacement Battery (B-T5)
The B-T5 is a 3.87V, 5900mAh (22.83Wh) Li-Polymer cell for the Vivo Y55s, Y55s 5G 2021, and V2164A. It slots into the same physical bay as the original and connects to the same charge IC and fuel gauge. Capacity figure is taken directly from the product specification — not estimated from a third-party source.
- Y55s / Y55s 5G 2021 / V2164A fit: These three variants share the same 94.15 × 63.76 × 5.30mm battery bay, the same BMS connector pinout, and the same charge IC handshake. The B-T5 part number spans all three because the voltage rail and communication lines are identical across the range.
- Bench tested on actual hardware: We ran the B-T5 through a full charge-discharge cycle on a V2164A unit. The BMS accepted the cell without error flags, charge current ramped normally through CC into CV phase, and the fuel gauge registered a full state-of-charge on completion.
- First-cycle fast charge protocol: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard current. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's actual discharge curve before high-current charging pushes load into an uncalibrated cell.
Why the Y55s reports wrong battery percentage after a cell swap
The fuel gauge IC on the Y55s stores a learned discharge curve from the old cell. When a new cell goes in, the IC still references that old curve, so the percentage readout drifts from the actual state of charge. This shows up as the phone jumping from 40% to 10% with no warning, or sitting at 1% for an unusually long time. One full discharge-charge cycle at standard current forces the coulomb counter to reset and map the new cell's actual capacity curve. After that cycle, percentage reporting stabilises.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC has not yet recalibrated and the new cell hits a voltage cliff under modem or display load before the reported percentage reaches zero. The cell voltage drops below the BMS cutoff threshold — typically around 3.0V — while the OS still shows charge remaining. The fix is the same recalibration cycle: drain the phone to automatic shutdown, then charge uninterrupted to 100% at standard charge rate. After one complete cycle the fuel gauge maps the actual low-voltage cutoff point of the new cell and the premature shutdowns stop.