About this replacement
Vivo Z5 / V1921 — 3.85V Li-Polymer Replacement Battery (B-H3)
This is a 3.85V, 4400mAh (16.94Wh) lithium-polymer cell for the Vivo Z5 and V1921 smartphones. It replaces OEM part number B-H3 and fits the same connector and battery bay as the original. Use this when the stock cell no longer holds a usable charge or the phone shuts off unexpectedly under load.
- Z5 and V1921 platform fit: Both models share the same PCB battery connector, BMS handshake protocol, and physical bay dimensions — 86.70 × 62.80 × 4.60mm. One cell part number covers both.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Z5 platform. The BMS accepted the cell without triggering fault flags, and the charge IC stepped through trickle, CC, and CV phases correctly at standard current.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one full discharge-to-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.
Sudden shutdown at 20–30% on the Vivo Z5 after a cell swap
This is a voltage cliff, not a capacity fault. Under modem or display load, cell voltage sags below the BMS cutoff threshold before the fuel gauge reaches zero. The old cell's discharge curve is still stored in the coulomb counter, so the reported percentage is ahead of actual voltage. One full uninterrupted discharge cycle — from 100% to auto-shutdown — then a full charge resets the counter against the new cell's real curve. After that cycle, shutdowns at 20–30% typically stop.
USB fast charge not activating on the first cycle after replacement
The charge IC on the Z5 runs a handshake with the BMS before stepping up to fast-charge current. On a fresh cell with no charge history, some units hold the IC in standard 5V/1A mode through the first full cycle as a precaution. This is not a fault with the replacement cell. Let the first charge complete at standard current — subsequent sessions will negotiate fast-charge rates normally once the BMS registers a completed cycle. Confirm fast charge is active by checking the charging notification in Settings → Battery.