About this replacement
Vivo IQOO Z8 — 7.74V Li-Polymer Replacement Battery (BA03)
This is a 7.74V, 2400mAh (18.58Wh) Li-Polymer replacement battery for the Vivo IQOO Z8 smartphone. It fits the BA03 OEM part number slot directly. Use it to restore power when the original cell has degraded, swells, or no longer holds charge.
- IQOO Z8 fit: The IQOO Z8 uses a dual-cell Li-Polymer pack at a 7.74V nominal rail. The BA03 battery matches that voltage configuration and the BMS handshake the phone's charge IC expects. Fitting a mismatched voltage cell will cause the charge IC to reject the pack entirely.
- Bench tested on actual hardware: We cycled this battery through charge and discharge on the IQOO Z8 platform and confirmed the BMS communicates correctly with the phone's fuel gauge IC. The charge IC accepted full protocol negotiation without lockout on the second cycle.
- First-cycle fuel gauge reset: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard speed. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging begins on an uncalibrated cell.
Sudden shutdown at 20–30% on the replacement cell
This happens because the fuel gauge IC is still using the discharge curve from the old, degraded cell. When modem activity or screen-on load spikes current draw, the new cell's voltage drops faster than the IC expects at that state of charge. The IC sees what it thinks is an undervoltage condition and triggers a protective shutdown before the battery is actually empty. One full discharge-charge cycle at standard speed recalibrates the coulomb counter and eliminates most of these false shutdowns.
USB-PD fast charge not engaging on the first cycle after replacement
On the first cycle, the BMS in a new cell may not complete the handshake required for the phone to negotiate fast charge protocols. The charge IC defaults to standard 5V input rather than risk pushing high current into an unverified cell. Complete one full charge at standard speed first. After that cycle, fast charging should engage normally when the BMS and charge IC have exchanged authentication data.