About this replacement
Vivo V2284A / S17 Pro 5G — 3.91V Li-Polymer Replacement Battery (B-Z8)
The B-Z8 is a 3.91V, 4500mAh (17.6Wh) lithium-polymer cell that fits the Vivo V2284A and S17 Pro 5G smartphones. Both devices share the same battery bay geometry, connector pinout, and BMS handshake protocol, so one cell covers both models. This replacement restores full charge capacity when the original cell has degraded through normal charge cycles.
- V2284A and S17 Pro 5G fitment: These two models run the same battery bay dimensions, the same four-pin connector, and the same BMS communication line. The fuel gauge IC on both boards reads cell chemistry from the same register set, so the B-Z8 handshakes correctly on either device without triggering a compatibility warning.
- Bench tested on actual hardware: We cycled the B-Z8 through charge and discharge on the bench, confirmed the BMS accepted the cell without flagging an over-voltage or under-voltage fault, and verified the coulomb counter initialised correctly on the first full cycle.
- First-cycle fast charge caution: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC recalibrate its discharge curve against the new cell before high-current fast charging pushes current into an uncalibrated register — preventing erratic percentage readings from the first charge onward.
Why the S17 Pro 5G reports wrong battery percentage after a cell swap
The fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the B-Z8. The IC reads voltage, maps it against the old curve, and outputs an incorrect percentage to the OS. One complete slow discharge-charge cycle forces the coulomb counter to relearn the curve against the new cell. After that cycle, percentage reporting stabilises.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC is still calibrated to the old cell's discharge curve and the new cell hits a steeper voltage cliff under modem or screen load than the IC expects. The BMS triggers a hard cutoff the moment cell voltage drops below its protection threshold — even though the OS still shows charge remaining. The fix is the same recalibration cycle: discharge fully to auto-shutoff, then charge uninterrupted to 100% without fast charging. After one full cycle, the coulomb counter anchors to the correct low-voltage endpoint for the B-Z8 cell.